Etymology
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squab (n.)
1680s, "very young bird," earlier (1630s) "unformed, lumpish person" and used at various times for any sort of flabby mass, such as sofa cushions; probably from a Scandinavian word (compare dialectal Swedish skvabb "loose or fat flesh," skvabba "fat woman"), from Proto-Germanic *(s)kwab-. Klein lists cognates in Old Prussian gawabo "toad," Old Church Slavonic zaba "frog."
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pigeon (n.)

late 14c., pijoun, "a dove, a young dove" (early 13c. as a surname), from Old French pijon, pigeon "young dove" (13c.), probably from Vulgar Latin *pibionem, dissimilation from Late Latin pipionem (nominative pipio) "squab, young chirping bird" (3c.), from pipire "to peep, chirp," a word of imitative origin. As an English word it replaced culver (Old English culufre, from Vulgar Latin *columbra, from Latin columbula) and native dove (n.). 

The meaning "one easily duped, a simpleton to be swindled" is from 1590s (compare gull (n.2)). Pigeon-hearted (1620s) and pigeon-livered (c. 1600) are "timid, easily frightened." A pigeon-pair (by 1800) are twins of the opposite sex (or family consisting of a boy and a girl only), so called because pigeons lay two eggs, normally hatching a male and a female.

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squabble (n.)
c. 1600, probably from a Scandinavian source and of imitative origin (compare dialectal Swedish skvabbel "a quarrel, a dispute," dialectal German schwabbeln "to babble, prattle"). The verb also is from c. 1600. Related: Squabbled; squabbling.
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