oper

The root oper comes from Latin opus (plural opera), meaning "a work" — both the act of working and the thing produced by working. Its verb form operārī meant "to labor, to be busy with work." From the very start, opus carried this double life: it could be the effort you put in, or the finished result that effort created.

That double meaning splits the family into two clear branches.

Branch 1 — work as activity (operārī → operate). When you operate a machine, you are literally "making it work." Add suffixes and you get the whole functional family:
- operate — to work, to function, to run something
- operation — the working of something (a business operation, a math operation, a surgical operation)
- operator — the person doing the working (a crane operator, a phone operator)
- operational — in working condition, up and running
- operative — actually working / effective ("the operative word")

Branch 2 — work as product (opus → opus / opera). Here opus stays a noun meaning "a created work," especially an artistic one:
- opus — a single composition, numbered in a composer's output (Beethoven's Opus 27)
- operetta — a little opus, a short light opera (Italian diminutive -etta)

The most productive prefix is co- (together). Co- + operārī = "to work together":
- cooperate / cooperation / cooperative — all about laboring side by side toward one goal

One surprising member is maneuver (British: manoeuvre). It comes from manū operārī, "to work by hand" — manus (hand) fused with operārī. Originally it meant simple handiwork; through French manœuvre it climbed in skill and stakes to mean a precise, controlled movement — first of ships and armies, now any clever tactical move.

The pattern to remember: every oper- word is about work — either the doing of it (operate, cooperate) or the result of it (opus, operetta).