"O frabjous day! Callooh! Callay!"
A portmanteau word coined, alongside many others, by Lewis Carroll in the poem-within-a-book, Jabberwocky (from Through the Looking Glass). Frabjous appears to be the result of leaving fabulous and joyous in a motel room overnight with a bottle of champagne and some oysters. To convey the essence of the word more effectively, you might define it as fabulous multiplied by joyous. It is truly a frabjous word.
(Martin Gardner devotes seven pages of marginalia to Jabberwocky in The Annotated Alice, but doesn't mention frabjous. This is probably because its meaning is clear and direct enough. A shame to dissect something so... well, frabjous.)