英语词源字典 - 在线词源网站

sparingly (adv.)[sparingly 词源字典]: mid-15c., from sparing, attested from late 14c. as a present participle adjective from spare (v.), + -ly (2).[sparingly etymology, sparingly origin, 英语词源]
unsparing (adj.): "showing no mercy," 1580s, from un- (1) "not" + sparing, attested from late 14c. as a present participle adjective from spare (v.). Meaning "profuse" is from 1660s. Related: Unsparingly.