An Etymological Dictionary of the German Language/tief
tief, adj., ‘deep, profound, low,’ from the equiv. MidHG. tief, OHG. tiof; corresponding to OSax. diop, Du. diep, AS. deóp, E. deep (depth and to dip), OIc. djópr, and Goth. diups, ‘deep.’ The common Teut. adj. diupa-, of which ModHG. taufen is a factitive, belongs to a Teut. root dū̆p, the variant of which, dū̆b, appears in AS. dŷfan, E. to dive (see Taube), as well as in E. dub. Comp. W. dwfn, OIr. fudomain, Lith. dubùs, ‘deep, hollow,’ OSlov. duplĭ, ‘hollow’ (see Tobel), from an Aryan root dhub, dhup. For a nasalised Teut. root dump, see Tümpel.