A dish that a vegetarian could safely order: melted cheese poured over toast or crackers.
The name may have originated among the English as a dig against their neighbors, the Welsh. Rabbit was a much more expensive dish than cheese and toast, but if you were Welsh, that's probably what you made do with.
Since there is no rabbit at all in this dish, folk etymology created the variant Welsh rarebit, which upgrades it from a poor man's dish to a purported delicacy.
Photo: adactio from Flickr