c. 1300, "without knowledge, ignorant," from un- (1) "not" + present participle of know (v.). Noun meaning "ignorance" is mid-14c., especially in phrase cloud of unknowing, title of a medieval book of Christian mysticism. Related: Unknowingly. A verb unknow "fail to recognize" is attested from late 14c.[unknowing etymology, unknowing origin, 英语词源]