precaution n.

word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."

The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.

c. 1300, caucioun, "bail, guarantee, pledge," from Old French caution "security, surety" (13c.), from Latin cautionem (nominative cautio) "caution, care, foresight, precaution," noun of action from past-participle stem of cavere "to be on one's guard" (from PIE root *keu- "to see, observe, perceive").

The Latin sense re-emerged in English as "prudence in regard to danger" (1650s). The meaning "word of warning, monitory advice" is from c. 1600. The meaning "anything which excites alarm or astonishment" is U.S. slang, 1835.