1630s, "closely acquainted, very familiar," also "inmost, intrinsic," from Late Latin intimatus, past participle of intimare "make known, announce, impress," from Latin intimus "inmost, innermost, deepest" (adj.), also used figuratively, of affections, feelings, as a noun, "close friend;" superlative of in "in" (from PIE root *en "in"). Intimate (adj.) used euphemistically in reference to women's underwear from 1904. Related: Intimately.
1530s, "make known formally;" 1580s, "suggest indirectly," back-formation from intimation (which could explain the pronunciation) or else from Late Latin intimatus, past participle of intimare "to make known." The Old French verb was intimer. Related: Intimated; intimating.
1650s, "familiar friend, person with whom one is intimate," from intimate (adj.). Sometimes 17c.-19c. in false Spanish form intimado. Latin intimus had a similar noun sense. Intimates as a commercial euphemism for "women's underwear" is from 1988.