Yours, Etc.: Origins and Uses of 8 Sign-Offs
1680s, "very young bird," earlier (1630s) "unformed, lumpish person" and used at various times for any sort of flabby mass from sea slugs to sofa cushions; probably from a Scandinavian word (cf. dialectal Swedish skvabb "loose or fat flesh," skvabba "fat woman"), from Proto-Germanic *(s)kwab- (cf. Old Prussian gawabo "toad," Old Church Slavonic zaba "frog").