The word 'stocky' originates from the Middle English period, formed by adding the descriptive suffix '-y' to the noun 'stock'. The core meaning of 'stock' in Old English and other Germanic languages referred to a tree trunk, post, or stem—something solid, sturdy, and fundamental. By the 16th century, this concrete sense evolved metaphorically to describe the main stem or lineage of a family (as in "family stock") and a stored supply of goods. The adjective 'stocky', emerging in the early 19th century, directly channels the original, physical sense of solidity and thickness inherent in a tree trunk. It applies this quality to describe a human or animal build that is broad, solid, and sturdy, much like the robust form of a tree stump or a thick post.

This word is a simplex form. It is derived from the English noun 'stock' (meaning trunk, stem, source, supply) combined with the adjectival suffix '-y'. The root 'stock' is of Germanic origin (Old English 'stocc', meaning tree trunk, log, post).