v. (-ies, -ied) 1 tr. & intr. make or become less dense or solid (rarefied air). 2 tr. purify or refine (a person's nature etc.). 3 tr. make (an idea etc.) subtle. rarefaction n. rarefactive adj. rarefication n.
[ ME f. OF rarefier or med.L rarificare f. L rarefacere f. rarus rare + facere make ]