1546, from L.
fabulosus "celebrated in fable," from
fabula (see
fable). From "mythical," sense of "incredible" first recorded 1609. Slang shortening
fab first recorded 1957; popularized in reference to The Beatles, c.1963.
"Fabulous (often contracted to fab(s)) and fantastic are also in that long list of words which boys and girls use for a time to express high commendation and then get tired of, such as, to go no farther back than the present century, topping, spiffing, ripping, wizard, super, posh, smashing." [Fowler, 1965]