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early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for first element see know. Second element obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock. Meaning "capacity for knowing, understanding; familiarity; fact of knowing" is late 14c. Sense of "an organized body of facts or teachings" is from c.1400, as is that of "sexual intercourse." Also a verb in Middle English, knoulechen "acknowledge" (c.1200), later "find out about; recognize," and "to have sexual intercourse with" (c.1300).