An Etymological Dictionary of the German Language/fast

by Friedrich Kluge

fast, adv., ‘almost, nearly,’ from MidHG. vaste, vast, adv. (from vęste, ‘firm’), ‘firmly, strongly, powerfully, very, very quickly,’ OHG. vasto, adv., from fęsti; similar unmutated advs. from mutated adjs. are schon from schön, spat from spät. ModHG. has also turned fest into an adv., the older adv. fast having been specialised in meaning; even in MidHG. vęste is an adv.