unauˈthentically,adv. (un-1 11.) 1600W. Watson Decacordon ix. x. (1602) 332 A maxime in the lawes, either vnauthentically defined, or remaining litigious.1975Daily Tel. 17 Mar. 10/2 John Constable's amusingly, if probably unauthentically, informal continuo-comments.