precaution (n.) Look up precaution at Dictionary.com
c.1600, from French précaution (16c.) and directly from Late Latin praecautionem (nominative praecautio) "a safeguarding," from past participle stem of Latin praecavere "to guard against beforehand," from prae "before" (see pre-) + cavere "to be one's own guard" (see caution (n.)). The verb meaning "to warn (someone) in advance" is from c.1700.