"previous caution, prudent foresight (to prevent mischief or secure good results); a measure taken beforehand, an act of foresight," c. 1600, from French précaution (16c.) and directly from Late Latin praecautionem (nominative praecautio) "a safeguarding," noun of action 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.)). In mid-20c. a euphemism for "contraception." The verb meaning "to warn (someone) in advance" is from c. 1700.
adjective and noun word-forming element, in most cases from Latin -arius, -aria, -arium "connected with, pertaining to; the man engaged in," from PIE relational adjective suffix *-yo- "of or belonging to." The neuter of the adjectives in Latin also were often used as nouns (solarium "sundial," vivarium, honorarium, etc.). It appears in words borrowed from Latin in Middle English. In later borrowings from Latin to French, it became -aire and passed into Middle English as -arie, subsequently -ary.
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Definitions of precautionary
taken in advance to protect against possible danger or failure;