Definition of "locum"

"I asked about his Joes, he said the Joes could look after themselves and if Jack was bothered about them he could send a locum."

1986, John le Carré, A Perfect Spy

-- "I suppose you wouldn't like to do a locum for a month on the South coast? Three guineas a week with board and lodging." -- "I wouldn't mind," said Philip. -- "It's at Farnley, in Dorsetshire. Doctor South. You'd have to go down at once; his assistant has developed mumps. I believe it's a very pleasant place."

1915, W.S. Maugham, Of Human Bondage, chapter 116