Mid 16th century: perhaps a shortening of obsolete fible-fable 'nonsense', reduplication of fable.

• fabulous from Late Middle English:

  The Latin word fabula ‘story’, ultimately from fari, meaning ‘to speak’, is the source of both fabulous and fable (Middle English), and perhaps of fib (mid 16th century), which may be a shortening of the obsolete fible-fable ‘nonsense’. A fable is a short story which conveys a moral, and is particularly associated with the legendary 6th-century bc Greek storyteller Aesop, whose fables have given the language many expressions (see, for example, at chicken). In early use fabulous meant ‘known through fable’ or ‘not based on fact’. The idea of ‘astonishing’ led to it being understood as both ‘beyond belief’ and ‘wonderful, marvellous’. As the 60s started to swing, fabulous was shortened to fab, and the Beatles were nicknamed the Fab Four, while in the 1990s TV comedy Absolutely Fabulous (sometimes shortened to Ab Fab), ‘Fabulous, sweetie!’ was the standard encouragement. See also fate