reverse

Charles Lamb writes in 1808 of Stephen growing rich "by a reverse of fortune." That phrase shows the noun at its most natural: a turn back, often in someone's luck. Note that Lamb's turn is a lucky one. The "setback" meaning took the same word in the opposite direction.

A setback with a slightly elevated, historical ring, at home in accounts of war, careers and fortunes. The idiomatic verb is "meet with": Peter Hopkirk's The Great Game (1990) says the British "had met with a reverse." It counts freely, so a life can hold many reverses. Shelley's "such sad reverse" shows it once used without an article in verse.

A sense of political and moral upheaval found in early eighteenth-century writing. In Alexander Pope's version of Statius, rivals "divide, and these reverse, the state." John Rogers writes that custom "reverses even the distinctions of good and evil." The object is something established, such as a state or a moral order, and the meaning is to overturn it, not merely to send it backward.

Software analysts shortened reverse-engineer to plain reverse, and the -ing form, reversing, became the name of the whole craft. Eldad Eilam's 2011 book is titled Reversing: Secrets of Reverse Engineering. Christopher C. Elisan's Malware, Rootkits & Botnets (2012) shows how much the term is used in work on malicious software. Its forms follow the ordinary verb: reversed, reversing.

In chemistry the word describes a change of direction, not of substance: what was made is turned back into what it was made from. The tools are the conditions of the reaction, such as concentration, temperature and pressure. A chemist therefore speaks of reversing a reaction by shifting those conditions.

Graph theorists have two names for one object: the reverse of a directed graph is also called its transpose. It keeps every vertex and flips every edge, so an edge from u to v becomes one from v to u, and sources and sinks trade places. Either name is correct.

A fencing term from the Elizabethan stage. In William Shakespeare's The Merry Wives of Windsor (c. 1597), it appears in a run of jargon: "thy punto, thy stock, thy reverse." What makes the stroke a reverse is the backhanded turn of the hand, which sets it apart from a straight thrust.

Surgical bandaging uses the reverse to keep a roller bandage lying flat where a limb changes width, such as along the calf or forearm. Each fold turns the strip back on itself and sends it off at a new angle. As a result, the wrap follows the taper of the limb instead of gaping or bunching.

In aviation the object is the engine, not the aircraft: a crew reverses one or both engines. The effect is reverse thrust, which redirects the engine's output forward so that the force works against the plane's motion. It slows the aircraft on the ground after landing.

Railway signaling names the two positions of a set of points plainly: normal for the default route, reverse for the other. The word usually follows its noun or comes after a verb, as in the points are reverse or with the points reverse. It describes a setting of the track, not a direction of travel. Only the route changes.

Signalers turn a position name into a verb: to reverse the points is to set them to reverse, onto the diverging route, while the other position is called normal. The object is the points, not the train. When the points move on their own, the verb becomes intransitive, as in the points' own movement.

Botanical description uses it as a straight equivalent of reversed, as in a reverse shell. That fits its history: Latin reversus was itself a past participle, so the shorter form meant "reversed" before English ever added an -ed. Outside technical description, reversed is the safer choice for anything turned the opposite way.

Genetics borrows the word for a step that runs against the usual flow of genetic information. Here an RNA template is copied into complementary DNA, or cDNA. It is best known from the fixed phrases reverse transcription and reverse transcriptase, the enzyme that does the copying. It is rarely used on its own before other nouns.

A rare, poetic adverb today. Donal Serrell Thomas could still use it in 1963 for an imagined world that runs the wrong way round, but everyday English says in reverse, backward or upside-down. The word follows the verb directly, with no -ly ending, and that bare form gives it an old-fashioned ring. Keep it for verse or deliberate archaism.

A verb to recognize when reading, not one to use. It takes no object and means simply to come back. Spenser uses it in The Faerie Queene (1590), spelled reuerse, asking whether the dead only sleep "and shall againe reuerse": that is, return to life. A modern reader can easily mistake it for turning around or for backing a vehicle up, so read it as "return" wherever it appears.

The transitive counterpart of the obsolete "return" sense, from the same poem by Spenser. In it, an old dame works to drive "out of her daughter's heart fond fancies to reverse." The construction pairs the verb with a place the thing is driven out of. Like its partner, it is obsolete; today you would say turn away or drive off.