"servile parasite," 1826, apparently shortened from toad-eater "fawning flatterer" (1742), originally (1620s) "the assistant of a charlatan," who ate a toad (believed to be poisonous) to enable his master to display his skill in expelling the poison. The verb is recorded from 1827. Related: Toadied; toadying.
[toady etymology, toady origin, 英语词源]