(countable) A thick cushion, especially a flat one covering the seat of a chair or sofa.
a.1744, Alexander Pope (imitating Earl of Dorset), Artemisia, 1795, Robert Anderson (editor), A Complete Edition of the Poets of Great Britain, page 86,
On her large ſquab you find her ſpread, / Like a fat corpſe upon a bed, / That lies and ſtinks in ſtate.
[H]erds of shabby vampires, Jew and Christian, over-run the house, [...] punching the squabs of chairs and sofas with their dirty fists, touzling the feather-beds, opening and shutting all the drawers, balancing the silver spoons and forks, looking into the very threads of the drapery and linen, and disparaging everything.
The eagle took the tortoise up into the air, and dropped him down, squab, upon a rock.
Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing. (See the entry for “squab”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.:G. & C. Merriam, 1913, →OCLC.)