acknowledge v.

early 12c., cnawlece "acknowledgment of a superior, honor, worship;" for the first element see know (v.). The second element is obscure, perhaps from Scandinavian and cognate with the -lock "action, process," found in wedlock.

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." The 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.

Since Knowledge is but sorrow's Spy,

   It is not safe to know.

[Davenant, song from "The Just Italian," 1630]

"in a position above and in contact with; in such a position as to be supported by;" also noting the goal to which some action is or has been directed; "about, concerning, regarding; in a position to cover;" as an adverb, "in or into a position in contact with and supported by the top or upper part of something; in or into place; in place for use or action; into movement or action; in operation," Old English on, unstressed variant of an "in, on, into," from Proto-Germanic *ana "on" (source also of Dutch aan, German an, Gothic ana "on, upon"), from PIE root *an- (1) "on" (source also of Avestan ana "on," Greek ana "on, upon," Latin an-, Old Church Slavonic na, Lithuanian nuo "down from").

Also used in Old English in many places where we now would use in. From 16c.-18c. (and still in northern England dialect) often reduced to o'. Phrase on to "aware" is from 1877.