Nobody knows where the word came from. It appeared in English in the 1550s with no clear ancestor.
The origin of the English word job is unknown. It appeared in the 1550s meaning a piece of work, a task, a specific thing to be done, without a clear etymological ancestor in French, Latin, or any other source language.1 Some scholars have suggested a connection to the Middle English gobbe, meaning a lump or mouthful, but the link is speculative.
For its first three centuries, job meant a specific task, not a permanent position. A person did jobs. A person did not have a job. The phrase "a steady job" would have been puzzling to an English speaker in 1600, because the word implied precisely the opposite: something temporary, discrete, and bounded.2
The modern meaning, a regular position of employment, solidified during the nineteenth century as the industrial economy created permanent wage positions that needed a name. The word that had described a lump of work, something you picked up and put down, became the word for the central organizing fact of adult life.3
English now uses the same word for a task, a role, an identity, and a moral obligation. Four meanings in a single syllable, all descended from a word whose origins no one can trace. The most important word in the vocabulary of modern work arrived from nowhere.4