The Collaborative International Dictionary of English v.0.48:

Squab \Squab\, adv. [Cf. dial. Sw. sqvapp, a word imitative of a
   splash, and E. squab fat, unfledged.]
   With a heavy fall; plump. [Vulgar]
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         The eagle took the tortoise up into the air, and
         dropped him down, squab, upon a rock.    --L'Estrange.
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The Collaborative International Dictionary of English v.0.48:

Squab \Squab\ (skw[o^]b), a. [Cf. dial. Sw. sqvabb a soft and
   fat body, sqvabba a fat woman, Icel. kvap jelly, jellylike
   things, and E. quab.]
   1. Fat; thick; plump; bulky.
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            Nor the squab daughter nor the wife were nice.
                                                  --Betterton.
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   2. Unfledged; unfeathered; as, a squab pigeon. --King.
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The Collaborative International Dictionary of English v.0.48:

Squab \Squab\, n.
   1. (Zool.) A nestling of a pigeon or other similar bird, esp.
      when very fat and not fully fledged.
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   2. A person of a short, fat figure.
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            Gorgonious sits abdominous and wan,
            Like a fat squab upon a Chinese fan.  --Cowper.
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   3. A thickly stuffed cushion; especially, one used for the
      seat of a sofa, couch, or chair; also, a sofa.
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            Punching the squab of chairs and sofas. --Dickens.
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            On her large squab you find her spread. --Pope.
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The Collaborative International Dictionary of English v.0.48:

Squab \Squab\, v. i.
   To fall plump; to strike at one dash, or with a heavy stroke.
   [Obs.]
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WordNet (r) 3.0 (2006):

squab
    adj 1: short and fat [syn: squab, squabby]
    n 1: flesh of a pigeon suitable for roasting or braising; flesh
         of a dove (young squab) may be broiled [syn: squab,
         dove]
    2: a soft padded sofa
    3: an unfledged pigeon

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "squab":
   Cornish hen, avifauna, baby bird, bear, bird, bird of Jove,
   bird of Juno, bird of Minerva, bird of night, bird of passage,
   bird of prey, birdie, birdlife, birdy, broiler, cage bird, caille,
   canard, caneton, capon, chapon, chick, chicken, crowd, crush,
   cygnet, dindon, diving bird, dove, duck, duckling, dumpy, eagle,
   eaglet, faisan, fish-eating bird, fledgling, flightless bird, fowl,
   fruit-eating bird, fryer, fulmar, game bird, goose, grouse,
   guinea hen, insect-eating bird, jam, migrant, migratory bird,
   nestling, oie, oscine bird, owl, partridge, passerine bird,
   peacock, peafowl, peahen, perching bird, pheasant, pigeon,
   pigeonneau, poulet, push, quail, ratite, roaster, sea bird,
   seed-eating bird, shore bird, slop, songbird, squash, squeeze,
   squish, stewing chicken, storm petrel, stormy petrel, stubby,
   stumpy, swan, thick, thickset, turkey, volaille, wading bird,
   warbler, water bird, waterfowl, wild duck, wildfowl