undeˈceiver [f. undeceive v.] One who or that which undeceives. 1643(title), The Vn-Deceiver.1668R. L'Estrange Vis. Quev. (1708) 114 Some call me the Plain-Dealer; others, the Undeceiver General.1825Lytton Falkland 20 My manhood has been the undeceiver of my youth.