c. 1300, "by God's grace," from gracious + -ly (2). Meaning "favorably, with good will" is late 14c.
Entries linking to graciously
gracious adj.
c. 1300, "filled with God's grace," from Old French gracios "courteous, pleasing, kind, friendly" (12c., Modern French gracieux), from Latin gratiosus "enjoying favor, agreeable, obliging; popular, acceptable," from gratia "favor" (from suffixed form of PIE root *gwere- (2) "to favor"). Meaning "merciful, benevolent" is from late 14c. As an exclamation, elliptically for gracious God, attested from 1713.
-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.