loop
Pluralloops
Pluralloops
- 1A length of thread, line, or rope doubled over so that it forms an opening.
He tied a loop at the end of the rope to secure the tent.
The sailor threaded the line through a small loop near the mast.
Note
The original knot behind every other meaning: Middle English loupe, "noose", came from Old Norse hlaup, "a run", from hlaupa, "to leap". The Norse word named a running knot, one that slides along its own line, which is why the earliest loop was a noose. Here the word means the doubled cord itself, while the opening it makes is a separate use.
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- 5A strip of tape or film joined into a ring so it repeats continuously.
The animator joined the frames into a seamless loop for the title screen.
An old answering machine recorded the greeting onto a short loop.
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- 7In computer programming, a set of instructions that keeps repeating until, or for as long as, a given condition holds.
The programmer used a loop to process every record in the file.
An infinite loop froze the application until it was forced to quit.
Note
Programmers usually name the controlling test as part of the word. A while loop runs as long as its condition holds, and an until loop runs until its condition becomes true. The classic failure is the infinite loop, whose condition never stops it. The verb for causing one grew out of exactly that failure.
- 8To move along a circular or curving path that returns on itself.
The roller coaster looped twice before the final drop.
Swallows loop through the barn and out the open doors.
Similarcircle, swoop, wheel, spiral, whirl
Note
The intransitive verb travels across very different fields: a program loops until the user presses a key, and in rugby a looping pass arcs out to a runner. That present participle, looping, often works as an adjective. Used that way, it describes a curved, arching movement rather than a complete circle.
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- 13A complete circuit around which an electric current can flow.
Engineers traced the current around the loop to find the fault.
A single loop in the simple circuit carried the entire load.
Similarcircuit
- 14An aerobatic maneuver in which an aircraft flies a complete circle in a vertical plane.
The display pilot completed a perfect loop above the runway.
A tight loop demands precise control of speed and throttle.
- 15A bus, rail, or walking route that begins and ends at the same point.
The downtown loop connects all the major stations.
Riders can stay on the loop for as long as they like.
Note
Transit planners use the word for a route that needs no separate return leg: the bus or tram runs round the circuit and arrives back where it began. The word usually follows a place or kind of route, as in a downtown loop or a walking loop. The curve of track a train turns on at the end of a line is the terminal turning loop, a different thing.
- 16To fly an aircraft through a complete vertical circle as an aerobatic maneuver.
The display pilot looped his biplane twice before landing.
Competitors must loop the aircraft cleanly to score well.
- 17To connect electrical components together so as to complete a circuit.
She looped the sensor into the main circuit before testing it.
Technicians loop the components carefully to avoid loose connections.
Similarwire, connect, link, join
Oppositedisconnect
- 18A path whose starting point and ending point are one and the same.
The proof considers a loop that returns to its base point.
Every loop on a sphere can be shrunk down to a single point.
Note
Topologists fix a loop at a base point and then ask whether it can be shrunk continuously down to that point without leaving the space. On a sphere every loop can be shrunk this way. Unlike the graph-theory edge, this loop is a continuous path through a space, not a single connection between points.
- 19An edge that joins a vertex to itself.
The graph contains a loop at vertex three.
Removing the loop leaves a simple graph with no repeated edges.
Note
Graph theorists treat this as the one edge that touches only a single vertex, and it adds two to that vertex's degree because both of its ends land there. It is a single edge, not a route. A closed path through several vertices is called a cycle instead. Graphs with no loops and no repeated edges are called simple.
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- 22To set or arrange something within a loop.
She looped the cable behind the desk to keep it tidy.
Loop the belt through each fastener before buckling it.
Similarthread, pass, run, wind, coil
Note
Railways give this verb its clearest use: a train is looped when it is put into a side loop to let another go by, and the verb is mostly met in the passive. Richard Clinnick reported in 2021 that trains often looped on their journey emit 14% to 20% more NOx and particulates than non-stop services. The track involved is the passing loop.
- 23The curved, arching flight given to a slowly spun delivery in cricket.
The spinner's loop drew the batsman forward into a false stroke.
Extra loop on the delivery made it dip sharply before the crease.
Note
Cricket talk praises a spinner for giving the ball loop. The higher the ball rises before it dips, the harder its length is for the batsman to judge. The word is used much like flight, often without an article (extra loop, plenty of loop), and it belongs to the slower bowlers.
- 24A flexible region connecting the more ordered elements of a protein's secondary structure.
The enzyme's active site sits within a flexible loop.
Mutations in the loop changed how the protein folds.
Note
Protein chemists use the word for the stretches of chain between helices and strands, the parts that are not locked into a repeating pattern. Because these regions bend easily, they often form part of binding or catalytic sites. As a result, a change in a loop can alter how a protein folds or what it holds on to.
- 25A quasigroup that also contains an identity element.
Every group is a loop, but not every loop is a group.
The multiplication table of a finite loop forms a Latin square with an identity row.
Note
Algebra places these structures between quasigroups and groups: a group is exactly a loop whose operation is associative. Without associativity, a product cannot be freely regrouped, and an element's left and right inverses may differ. Finite ones are easy to picture, because their multiplication tables are Latin squares in which one row and one column simply repeat the headings.
- 26A small, narrow opening, such as a slit in a defensive wall.
Defenders fired their crossbows through each loop in the rampart.
The tower's only daylight came through a single loop.
Note
An old architectural meaning, and the one Shakespeare uses in The First Part of Henry the Fourth (c. 1597): "stop all sight-holes, every loop from whence / The eye of Reason may pry in upon us." The loop here is something to look through, a narrow slit in a wall. Its longer form, loophole, is the word most readers now know.
- 27A curved section of track at a terminus that lets trains or trams turn around and travel back without reversing.
The streetcar circled the loop and returned along the same avenue.
Engineers built a loop so the train could change direction without a turntable.
Similarturnaround
Note
Railway builders lay this curve so a train can change direction at the end of the line without reversing. Andrew Martin's Underground Overground (2012) describes Wood Lane, a station opened in 1908 on a terminal track loop for exactly that purpose. The shape explains the alternative names balloon loop and turning loop. Don't confuse it with the passing loop, which lets trains pass rather than turn.
- 28A short length of parallel track on a single-track line where one train can wait for another to pass.
The local train pulled into the loop to let the express through.
Without a loop on this branch, only one train could run at a time.
Similarsiding
Note
On a single-track railway, the loop is where trains meet. One train waits in it while another passes on the main line. Philip Haigh, writing in 2025, describes the line west of Salisbury as largely single-track since 1967, with a ten-mile loop between Templecombe and Yeovil and shorter ones at Chard and Axminster. Railway writers drop "passing" once the context makes it clear.
- 29Of a teacher, to advance through successive school years with the same group of students.
She looped with her class for three consecutive years.
Teachers who loop often build stronger relationships with families.
Note
Schools that practice looping keep a class with the same teacher for more than one year instead of reassigning it. The verb works with or without an object: a teacher loops with a class, or a school loops its classrooms. The arrangement also yields an adjective, as in the "looped classroom structures" of Lisa Lynn Snyder's An Investigation of Elementary Looping Practices (2003).
- 30A sports league; an organized association of competing teams.
He pitched three seasons in the bush loop before retiring.
Arellano formerly cavorted for the Galicias in the fast-paced National-American Soccer loop.
1963, “Italias Vie In Bayonne On Sunday”, in The Jersey JournalNote
Sports-page language from the United States and Canada calls a league a loop. The Jersey Journal in 1963 reported a player who had "formerly cavorted" in the National-American Soccer loop. The usage now sounds dated, so in ordinary writing choose league. Keep loop for a deliberately old-fashioned flavor.
- 31A spongy lump of hot iron taken from a furnace to be hammered into wrought iron, also spelled loup.
- 32To lay a second pipeline beside an existing one along the same route, to carry more.
Showing meanings only.
Practice
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Origin
From Middle English loupe ("noose, loop"), earlier lowp-knot, of North Germanic origin. It comes from Old Norse hlaup ("a run"), used in the sense of a "running knot," from hlaupa ("to leap"), ultimately from Proto-Germanic *hlaupaną ("to leap, run"). The verb is derived from the noun.