An Etymological Dictionary of the German Language/feist
feist, adj., ‘fat, in good condition,’ from MidHG. veiȥt, veiȥet, OHG. feiȥȥit, adj., ‘fat, greasy’; properly a partic. without gi-, ge- of a Goth. verb *faitjan, ‘to fatten,’ OHG. feiȥȥen, which is from the nominal stem faita-, ‘fat,’ OIc. feitr, MidHG. veiȥ. With the assumed Goth. *faitiþs are connected AS. fœ̂ted, fœ̂tt, and E. fat (comp. fett). Goth. *faita-, from pre-Teut. paido-, has no unquestionable cognates in the allied languages; it can scarcely be connected with OSlov. pitĕti, ‘to nourish, feed,’ on account of the faulty shifting of the dental (Slav. t corresponding to Goth. t is impossible); it is more probably related to the root πῖδ, ‘to swell, flow forth’; comp. πῖδαξ, ‘a spring,’ πιδύω, ‘to gush forth.’