labor (n.)
c.1300, "a task, a project;" later "exertion of the body; trouble, difficulty, hardship" (late 14c.), from Old French labor "labor, toil, work, exertion, task" (12c., Modern French labeur), from Latin laborem (nominative labor) "labor, toil, exertion; hardship, pain, fatigue; a work, a product of labor," of uncertain origin, perhaps originally from the notion of "tottering under a burden," and related to labere "to totter."

Meaning "body of laborers considered as a class" (usually contrasted to capitalists) is from 1839. Sense of "physical exertions of childbirth" is 1590s, earlier labour of birthe (early 15c.), a sense also found in Old French, and compare French en travail "in (childbirth) suffering" (see travail). Labor Day first marked 1882 in New York City.
labor (v.)
late 14c., "perform manual or physical work; work hard; keep busy; take pains, strive, endeavor" (also "copulate"), from Old French laborer "work, toil; struggle, have difficulty," from Latin laborare, from labor (see labor (n.)). The verb in modern French, Spanish, Portuguese means "to plow;" the wider sense being taken by the equivalent of English travail. Sense of "to endure pain, suffer" is early 15c., especially in phrase labor of child. Related: Labored; laboring.