job. (1) A low mean lucrative busy affair. (2) Petty, piddling work; a piece of chance work. [Johnson's Dictionary]
On the job "hard at work" is from 1882. Job lot is from obsolete sense of "cartload, lump," which might also ultimately be from gob. Job security attested by 1954; job description by 1920; job-sharing by 1972.