Welsh rabbityoudaoicibaDictYouDict[Welsh rabbit 词源字典]
Welsh rabbit: [18] Despite the proverbial liking of the Welsh for cheese, there is no known connection between Wales and the Welsh rabbit; it is thought the epithet may reflect an earlier humorous use of Welsh for inferior things or substitutes for the real thing (the use of one’s hand to comb one’s hair used to be known as the Welsh comb, for instance). But if the Welsh part of the compound is dubious, the rabbit part is downright impenetrable. All that can be said with reasonable certainly is that it is the original form (first recorded in 1725), and that rarebit (first recorded in 1785) is a later perversion by those who found rabbit a little vulgar.
[Welsh rabbit etymology, Welsh rabbit origin, 英语词源]