1640s, from intimate (adj.) + abstract noun suffix -cy. Sense of "sexual intercourse" attested from 1670s but modern use is from newspaper euphemistic use (1882).
Entries linking to intimacy
intimate adj.
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.
-cy
abstract noun suffix of quality or rank, from Latin -cia, -tia, from Greek -kia, -tia, from abstract ending -ia (see -ia) + stem ending -c- or -t-. The native correspondents are -ship, -hood.