An Etymological Dictionary of the German Language/dumm
dumm, adj., ‘stupid, silly,’ from MidHG. tum (gen., -mmes), tump (gen. -bes), ‘stupid, foolish, weak in understanding, dumb,’ OHG. tumb. In Goth. dumbs, OIc. dumbr the adj. is equiv. to AS. and E. dumb; the OHG. word, in addition to the meanings of MidHG., has likewise the signification ‘deaf,’ which also belongs to dumm in early ModHG. ‘Dull in sense and intellect’ may be the primary sense of the adj., which has not yet been found in the non-Teut. languages; stumm too has a peculiar history; see schmecken, hell. Words expressing the perceptions of one sense are often transferred to those of another. Hence Goth. dumbs, ‘dumb,’ OHG. tumb, ‘deaf, dumb,’ may possibly be allied to Gr. τυφλός, ‘blind’ (root dhubh; τυφ by the well-known rule for θυφ). This conjectural etymology is quite as uncertain as that offered under Dieb.