The origin of 'squab' is somewhat obscure, but it is thought to be an imitative or expressive formation from the early 17th century, possibly evoking the soft, fat, or squat appearance of a young bird. It first appeared in English referring to an unfeathered baby bird, particularly a pigeon. The sense was then extended metaphorically to describe a short, plump person, and subsequently used as an adjective meaning short and stout. This journey from a specific ornithological term to a descriptive word for human physique illustrates a common pattern of semantic broadening based on shared physical characteristics.

The word 'squab' is a simplex word of uncertain origin, likely imitative or expressive in nature. It is not productively formed from combinable morphemes in Modern English.