mid-13c., "abundant, plentiful," Middle English compound of ful "full" (see full (adj.)) + -som "to a considerable degree" (see -some (1)). Perhaps a case of ironic understatement. Sense extended to "plump, well-fed" (mid-14c.), then "arousing disgust" (similar to the feeling of having over-eaten), late 14c. Via the sense of "causing nausea" it came to be used of language, "offensive to taste or good manners" (early 15c.); especially "excessively flattering" (1660s). Since the 1960s, however, it commonly has been used in its original, favorable sense, especially in fulsome praise. Related: Fulsomely; fulsomeness.