The word 'tubby' is a straightforward English formation from the noun 'tub,' which originally referred to a broad, open wooden vessel. The adjective-forming suffix '-y' was appended to create a descriptive term meaning "resembling a tub" in shape. This literal comparison to a round, squat container was first applied humorously or affectionately to describe a stout, rotund body shape. Over time, the term softened from a purely physical descriptor to one often carrying a connotation of plumpness that is endearing or cuddly, especially in informal contexts.

Structure: tub (a wide container) + y (adjective-forming suffix) - tub: From Middle English 'tubbe', likely from Middle Dutch or Middle Low German 'tubbe', meaning a wooden vessel. Its functional role is as the core root, providing the semantic concept of a round, barrel-like container. - y: A native English suffix (from Old English '-ig', Proto-Germanic '-īgaz', Proto-Indo-European '-kos') used to form adjectives meaning "characterized by" or "full of."