An Etymological Dictionary of the German Language/schmeicheln
schmeicheln, vb., ‘to caress, coax, flatter,’ from MidHG. smeicheln, smeichen, ‘to flatter, praise, extol’; OHG. *smeihhen is wanting; comp. MidLG. smeken, Du. smeeken, ‘to implore’ (conversely, Du. vleijen signifies ‘to flatter’). These cognates, which have no corresponding terms in other languages, probably belong, like the words adduced under Schminke, to a Teut. and Aryan root smī̆-w, ‘to be insinuating, friendly,’ to which MidHG. smieren, smielen, ‘to smile’ (comp. Speichel from the root spîw, ‘to spit’), is allied. In that case E. to smile, Sans. smêra-s, ‘smiling,’ Sans. root smi, ‘to laugh,’ Lett. smët, ‘to laugh,’ and OSlov. směją, smijati sę, ‘to laugh,’ are probably allied. If from its relation to HG. glatt and E. glad it is assumed that the prim. meaning of the root smī̆-w is ‘to be smooth,’ the root smī̆ (see Schmied), ‘to work artistically’ (lit. ‘to do polished work’), may be regarded as cognate with the former; similarly OHG. gi-slihten signifies ‘to smooth over, polish,’ and ‘to flatter.’