Self-possession and calm control of oneself, especially in a trying situation.
Self-possession and calm control of oneself, especially in a trying situation — keeping it together.
Self-possession and the calm control of oneself, often outwardly displayed: it “implies the controlling of emotional or mental agitation by an effort of will or as a matter of habit.” The key contrast with equanimity (undisturbed inner evenness) is that composure can be effortful management of agitation present underneath — hence you “keep,” “lose,” or “regain” your composure, a state you sustain under threat of slipping rather than a permanent trait. Unlike serenity, tranquility, or calmness, it specifically implies a trying situation and the self-command not to break down.
c. 1600, originally “composition, arrangement,” from compose + -ure. The sense “calm, composed state of mind” is from the 1660s — the metaphor of a self that is well-arranged and settled rather than disordered.
A shift from “composing / arrangement” (c. 1600) to “composed, settled state of mind, calmness” by the 1660s. No reliable recent-generation shift.