'thick-walled' originates from English, specifically the combination of the adjective 'thick' + the noun 'wall' with the adjectival suffix '-ed', where 'thick' meant 'having relatively great depth or density' and 'wall' meant 'a vertical structure forming an enclosure or barrier'.

'thick' traces back to Old English 'þicce' meaning 'dense' or 'close', while 'wall' comes from Old English 'weall' (from Proto-Germanic *wallaz). The compound adjective 'thick-walled' is a straightforward Modern English formation by compounding these elements with '-ed' to express possession of thick walls.

Initially it described physical objects with notably thick walls; over time the phrase has occasionally been used metaphorically but has retained its core descriptive sense of 'having thick walls'.