imperturbable

Etymology

Came into English from Late Middle English imperturbable ("undisturbed; impossible to disturb"), borrowed from Late Latin imperturbābilis, from Latin im- (a variant of in-, a prefix meaning "not") plus Late Latin perturbabilis ("perturbable"), itself from Latin perturbō ("to confuse; to alarm, disturb, trouble, perturb") plus -bilis (a suffix forming adjectives denoting a capacity or worth of being acted upon). Perturbō in turn comes from per- (an intensifying prefix) plus turbō ("to agitate, disturb, unsettle, perturb; to upset"), from turba ("disorder, disturbance, turmoil"), possibly from Ancient Greek τῠ́ρβη (tŭ́rbē, "confusion, disorder, tumult"), itself either from Pre-Greek or from Proto-Indo-European *(s)twerH- ("to agitate, stir up; to urge on, propel"), plus -ō (a suffix forming infinitives of regular first-conjugation verbs). By surface analysis it breaks down as im- (a prefix meaning "not") plus perturbable.