From late 14c. as "capacity for knowing, understanding; familiarity;" also "fact or condition of knowing, awareness of a fact;" also "news, notice, information; learning; organized body of facts or teachings." Sense of "sexual intercourse" is from c. 1400. Middle English also had a verb form, knoulechen "acknowledge" (c. 1200), later "find out about; recognize," and "to have sexual intercourse with" (c. 1300); compare acknowledge.
c. 1300, matrimoine, "the married state, the relation of husband and wife, wedlock; the sacrament of marriage," from Old French matremoine "matrimony, marriage" and directly from Latin mātrimōnium "wedlock, marriage" (in plural "wives"), from mātrem (nominative māter) "mother" (see mother (n.1)) + -mōnium, suffix signifying "action, state, condition."
"formally wedded, united in wedlock, having a spouse," late 14c., past-participle adjective from marry (v.).
mid-15c., "of or pertaining to marriage, connubial, nuptial," from Old French matrimonial (14c.) and directly from Late Latin matrimonialis, from Latin mātrimōnium "wedlock, marriage" (see matrimony). Earlier as a noun meaning "a marriage" (late 15c.). Related: Matrimonially.