early 15c., "slowly and with difficulty," from laborious + -ly (2). Meaning "earnestly, strongly" is from c. 1500.
Entries linking to laboriously
laborious adj.
late 14c., "hard-working, industrious," from Old French laborios "arduous, wearisome; hard-working" (12c., Modern French laborieux), from Latin laboriosus "toilsome, wearisome, troublesome," also "inclined to labor, industrious," from labor "toil, exertion" (see labor (n.)). Meaning "costing much labor, burdensome" is from early 15c.; meaning "resulting from hard work" is mid-15c. Related: Laboriousness.
-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.