laborious adj.

c. 1300, "a task, a project" (such as the labors of Hercules); later "exertion of the body; trouble, difficulty, hardship" (late 14c.), from Old French labor "toil, work, exertion, task; tribulation, suffering" (12c., Modern French labeur), from Latin labor "toil, exertion; hardship, pain, fatigue; a work, a product of labor," a word of uncertain origin. Some sources venture that it could be related to labere "to totter" on the notion of "tottering under a burden," but de Vaan finds this unconvincing. The native word is work.

Meaning "body of laborers considered as a class" (usually contrasted to capitalists) is from 1839; for the British political sense see labour. Sense of "physical exertions of childbirth" is attested from 1590s, short for labour of birthe (early 15c.); the sense also is found in Old French, and compare French en travail "in (childbirth) suffering" (see travail). Labor Day was first marked 1882 in New York City. The prison labor camp is attested from 1900. Labor-saving (adj.) is from 1776. Labor of love is by 1797.

early 15c., "slowly and with difficulty," from laborious + -ly (2). Meaning "earnestly, strongly" is from c. 1500.