suspension

A mechanic's word for a whole system, not a single part. The springs, the shock absorbers and their links to the wheels together make up the suspension, so the word takes the singular. A speed bump pushes it upward from both tires at once. Drivers judge it by feel and call it stiff or soft. The name keeps the old idea of holding the car's body up above its wheels.

School discipline uses the word for a penalty rather than a precaution, which separates it from the workplace bar pending inquiry. Schools distinguish in-school suspension, where the student stays on campus under supervision, from the out-of-school kind, which keeps the student off the grounds altogether. The usual construction is suspension from school.

Chemistry draws its line between a suspension and a solution. Here the particles never dissolve, so they can be strained out or left to settle, and they are larger than a colloid's. The usual phrasing is spatial: matter is held in suspension, and when particles clump together and grow heavier, they fall out of suspension.

The core sense, and the one closest to the Latin: sub- "under" plus pendere "to hang", so a thing held up from beneath a support, like a load on a hook. Late Latin suspensio already meant "arching, vaulting" too. The step from hanging something up to holding it still in midair helps explain why the word also came to mean halting, as in a temporary stop.

In harmony the word names both the technique and the dissonance it produces. A held tone is first sounded as a consonance in one chord. It becomes the suspension when the harmony moves beneath it, and then it resolves: preparation, suspension, resolution. Composers write a suspension over the bass, and listeners hear the delay as tension, with the concord the ear expects held in the air.

Here the word belongs to Scots procedure. A party applies to the Lord Ordinary in the Court of Session to halt a sentence or a diligence before it is carried out. The order comes as letters of suspension, and counsel speak of seeking or obtaining a suspension. It works much like a stay, but the Scots name and procedure are its own.

Here the old Latin sense of hanging survives in geometric form: the space is strung between two points, one at each end. Topologists write it ΣX and build it as a quotient space of X × [0,1]. Suspensions make up an important class of H'-spaces. The same move, applied to maps instead of spaces, gives the suspension of a function.

The same construction applied to maps rather than spaces: a function from X to Y yields one from ΣX to ΣY, built on the suspended space. In the language of categories this becomes the suspension functor, written Σ, which the homotopy category of a pointed model category carries. Context usually tells you whether "a suspension" means the space or the map.