toadyoudaoicibaDictYouDict[toad 词源字典]
toad: [OE] Toad is a mystery word, with no known relatives in any other Indo-European language. Of its derivatives, toady [19] is short for the earlier toad eater ‘sycophant’ [17]. This originated in the dubious selling methods of itinerant quack doctors. They employed an assistant who pretended to eat a toad (toads were thought to be poisonous), so that the quack could appear to effect a miraculous cure with his medicine.

The toad-eating assistant came to be a byword for ‘servility’ or ‘dependency’, and hence for ‘servile flattery’. Toadstools [14] were named for their stool-like shape, and also because of an association between poisonous fungi and the supposedly poisonous toad.
[toad etymology, toad origin, 英语词源]
toad (n.)youdaoicibaDictYouDict
c. 1300, from late Old English tadige, tadie, of unknown origin and according to OED with no known cognates outside English. Applied to loathsome persons from 1560s. Toad-strangler "heavy rain" is from 1919, U.S. Southern dialectal.