Here's a proper etymology for Welsh rabbit/rarebit. Based on an old het-W parallel, It is simply a list of its ingredients in a Semitic language:
Hebrew Arabic
milk/cheese Het-Lamed-vet haleeb ale SHin-khaf-Resh toast Peh-Tof pita
Here's an etymology that may be useful :-)
Hebrew SHaKHaR = ale is probably related to the Latin name for a sugar- eating Brewer's yeast that causes fermentation: Saccharomyces cerevisiae.
A Semitic pun on this phrase explains the origin of the idiom: "hair of the dog that bit you". Using 3 for the letter aiyin (that used to have a G/K-sound as in 3aZa = Gaza), the Hebrew word for hair is Sa3aR, as in sacchar-. A Hebrew word for biting/eating is MinSHakh. Finally, the cerevisiae is similar to Cerebus, the 3-headed dog that guarded the descent to Hades ... cognate with Semetic KeLeB = dog. Hair + bite + dog => hair of the dog that bit you.
Spent brewer's yeast (found today in marmite/vegemite) was an ancient remedy for a hangover.
ciao, Israel "izzy" Cohen