toad + eater, said to allude to an old alleged practice among mountebanks, who would hire a boy to eat (or pretend to eat) toads, which many had considered poisonous. The toadeater (b.k.a. toady) would writhe in pain, until the quack gave him some "medicine", and then try to impress upon the crowd that the boy was cured. Compare toady.
toadeater (plural toadeaters)
- A fawning, obsequious parasite; a mean sycophant or flatterer.
- You're too zealous a toadeater, and betray yourself. — C. Dickens (1844).
- a chaplain, tutor, toadeater, or some superior servant. — J. Wilson (1819).
- A toad eater, a led captain, an humble companion, are appellations which no man, who has a real sense of honour, would chuse to possess; but these are the best names bestowed upon men who spend their lives in courting the great by all arts, but those of virtue and truth. V. Knox (1781). 
Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.