mid-15c., of persons; 1540s, of actions or objects, "likely to bring luck;" from luck (n.) + -y (2). Meaning "occurring by chance" is 1590s. Related: Luckier; luckiest; luckiness.
Lucky break is attested from 1884 in billiards; 1872 as "failure or break-down which turns out to be fortunate." Lucky accident is from 1660s. Lucky dog "unusually lucky person" is from 1842. Lucky Strike as the name of a U.S. brand of cigarettes (originally chewing tobacco) popular in the World War II years is said to date from 1871. Its popularity grew from 1935 when the brand's maker picked up sponsorship of radio's "Your Hit Parade."
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.
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Definitions of luckily from WordNet
by good fortune;
Synonyms: fortunately / fortuitously / as luck would have it