The word 'thickset' is a native English compound formed from two robust Old English roots. 'Thick' originally described density and closeness, extending from materials to crowds of people. 'Set' derives from the action of placing or establishing something firmly. When combined, the term literally describes something 'set thickly together.' This initially applied to densely planted hedges or closely arranged objects. By the 18th century, the logic of this literal meaning was applied figuratively to describe a human physique that appears densely and solidly built, as if the body's form is firmly set with broad proportions.

Structure: thick + set - thick: From Old English thicce (dense, viscous, numerous). In this compound, it conveys the sense of having a large or dense physical dimension. - set: From Old English sett (a place where something is set) and related to the verb settan (to cause to sit, place). In this compound, it conveys the sense of being placed, fixed, or built in a particular way.