"one who earns," in any sense, 1610s, agent noun from earn.

amount of money one makes (from labor or investment), 1732, from plural of verbal noun earning, from earn (v.). Old English had earnung in sense "fact of deserving; what one deserves; merit, reward, consideration, pay," but the modern word seems to be a new formation.

Old English esne "domestic slave, laborer, retainer, servant; youth, man," from Proto-Germanic *asnjoz- "harvestman" (source also of Gothic asneis), from *asanoz- "harvest" (see earn).

c. 1200, from un- (1) "not" + past participle of earn (v.). Unearned income is recorded from 1889.

1730, from well (adv.) + past participle of earn (v.).