hard-shell

The compound adjective 'hard-shell' is a transparent combination of two native English words. 'Hard' originates from the Proto-Germanic harduz, conveying the sense of solidity and strength, while 'shell' derives from Proto-Germanic skaljō, referring to a separating layer or covering, such as that of a nut or egg. Literally describing an organism with a rigid exoskeleton, like certain crustaceans or turtles, the term's logic was extended metaphorically. By the early 19th century, it began describing people with an inflexible, unyielding exterior, particularly in matters of doctrine or attitude, thus completing the journey from a physical descriptor to an abstract characterization of rigidity.

Structure: hard (firm) + shell (protective covering) - hard: From Old English 'heard' meaning "solid, firm, unyielding," of Germanic origin. - shell: From Old English 'sc(i)ell' meaning "hard outer covering," of Germanic origin.