固

Phono-semantic compound:

囗 — “to enclose” or “surround,” giving the sense of being fortified or contained;

古 — provides sound and also implies something time-worn or enduring.

Originally, 固 suggested “an enclosed old settlement” or a fortified, secure place. Over time, it extended metaphorically to solid or strong (physically or emotionally), and stubborn, rigid in one’s thinking.

Often appears in compounds like:

堅固 (견고) – solid, firm;

固執 (고집) – obstinate, stubborn;

固有 (고유) – inherent, native.