"wisely, with just discernment and prudence," c. 1400, from sage (adj.) + -ly (2).
Entries linking to sagely
sage adj.
"wise, judicious, prudent," c. 1300 (late 12c. as a surname), from Old French sage "wise, knowledgeable, learned; shrewd, skillful" (11c.), from Gallo-Roman *sabius, from Vulgar Latin *sapius, from Latin sapere "have a taste, have good taste, be wise" (from PIE root *sap- "to taste;" see sap (n.1)). Originally of persons, but that use is now poetic only or archaic; of advice, etc., "characterized by wisdom" is from 1530s. Related: Sageness.
-ly 2
common adverbial suffix, forming from adjectives adverbs signifying "in a manner denoted by" the adjective, Middle English, from Old English -lice, from Proto-Germanic *-liko- (cognates: Old Frisian -like, Old Saxon -liko, Dutch -lijk, Old High German -licho, German -lich, Old Norse -liga, Gothic -leiko); see -ly (1). Cognate with lich, and identical with like (adj.).
Weekley notes as "curious" that Germanic uses a word essentially meaning "body" for the adverbial formation, while Romanic uses one meaning "mind" (as in French constamment from Latin constanti mente). The modern English form emerged in late Middle English, probably from influence of Old Norse -liga.