The Collaborative International Dictionary of English v.0.48:
nippy \nippy\ adj. Pleasantly cold and invigorating; -- of weather conditions. Syn: crisp, frosty, nipping, snappy. [WordNet 1.5]WordNet (r) 3.0 (2006):
nippy adj 1: a sharp biting taste; "a nippy cheese" 2: pleasantly cold and invigorating; "crisp clear nights and frosty mornings"; "a nipping wind"; "a nippy fall day"; "snappy weather" [syn: crisp, frosty, nipping, nippy, snappy]