Traditionally the dish is a viscous liquid, normally poured or spooned. Classically the cheese used in Welsh rabbit is Lancashire, Cheddar or Double Gloucester, although Red Leicester is a popular substitute.
The Oxford English Dictionary states that it can also be "simply, slices of toasted cheese laid on toast", though this is more commonly known as cheese on toast.
The OED establishes that the original name of the food was "Welsh rabbit", and mentions "Welsh rarebit" only as an "etymologizing alteration of [the preceding]. There is no evidence of the independent use of rarebit". The source is not exactly known, but most likely was originally a slur. In the 17th and 18th centuries it was common in England to use the adjective "Welsh" for things of inferior quality, especially if these had been substituted for something better. This sense of "counterfeiting" may be connected with the use of "Welsh" or "Welch" as a verb meaning "to refuse or avoid paying money laid as a bet". The first record of the term "Welsh rabbit" was in 1725, with the alternative form "rarebit" occurring from 1785. In the Victorian era and later, however, the latter form became preferred in recipe books. This was based on folk etymology — "rabbit", that is, was assumed to be a perversion of earlier "rarebit", although the reverse was in fact true. Although "Welsh rabbit" is still heard, "Welsh rarebit" is the more commonly used form now.
Sometimes a slice of tomato is placed atop the cheese mixture before grilling. There are also a number of named derivatives. Perhaps because these are of recent origin, the spelling "rarebit" is commoner for them. The buck rarebit is a Welsh rabbit with a poached egg on top, the Irish rarebit is topped with onions, vinegar, herbs, and gherkins. There is the Yorkshire rarebit which is topped with both bacon and a poached egg. Other variations include the American rarebit which is a Welsh rabbit topped with whisked egg whites, and the English rarebit which uses red wine. A dish called Scotch rarebit exists, although this comes close to cheese (preferably Dunlop) on toast. The King rarebit is a normal Welsh rabbit with a fried egg on top.
This dish in some form is also common in other European countries. It is known as "Ramequin" or "Käseschnitte", although the French often use the term "Le Welsh", interestingly sometimes associated with Irish cuisine.
Cheese on toast
Cheese on toast is a simple snack dish prepared by putting cheese, usually sliced or grated, on top of bread and grilling it. Some people like to add onion, or extra flavouring, such as Brown sauce, Worcester sauce or tomato ketchup. The bread is usually unbuttered. Cheese on toast is distinguishable from Welsh rabbit since cheese is the only primary ingredient other than toast. Most commonly, cheddar cheese is used.
Some people do not distinguish between the two recipes and will call both cheese on toast or Welsh rabbit. Less common variations include using spreadable cheese.
Vivid nightmares are famously attributed to overindulgence in Welsh rabbit. This phenomenon is immortalized in Dreams Of A Rarebit Fiend, a series of comic strips written and drawn by Little Nemo creator Winsor McCay beginning in 1904. Each strip portrayed a nightmare experienced by a protagonist, a rabbit fiend who had made the poor choice of consuming too much rabbit before bedtime.
There is also a 1906 film based on McCay's comic strip named "Dreams of a Rarebit Fiend" by Edwin S. Porter, a special effects-filled journey through rabbit-induced nightmares. This film went on to inspire a Welsh rabbit-fueled nightmare sequence in the 1919 film "When the Clouds Roll By".
There was also an episode of Gomer Pyle, U.S.M.C. in which the Welsh Rabbit that Gomer consumes causes him to sleepwalk and verbally attack Sergeant Carter.