harden, set, clot, curdle
固 centers on becoming firm and stable: hardening, setting, clotting, or curdling. It describes a change from a softer or more fluid state into a solid, fixed form.
固 combines 囗 (enclosure) with 古, which likely contributes the sound and the idea of something old and solid. The enclosure reinforces the sense of something contained and hardened.
Inside an enclosure 囗, something old 古 sits and hardens over time. Picture an ancient object sealed in a container, slowly setting into a solid, firm mass.
For コ, imagine a hard, solid core inside the enclosure: core -> コ, and the old thing inside becomes the core of the hardened mass.
fixing (in place); being fixed (in place); securing; anchoring; fastening down
hardening; fortifying
to harden; to solidify
characteristic (of); peculiar (to); inherent (in); endemic; unique (to); native (to); intrinsic
stubborn; obstinate; pigheaded
firm; strong; solid; stable
sticking to (an opinion, theory, belief, etc.); clinging to; adherence; persistence; insistence
firm; determined; resolute; conclusive
to harden; to freeze; to strengthen; to solidify; to make (a fist); to tramp down (snow, dirt)
coagulation; freezing; solidification
solid (body); solid matter; solid-state
solid (body)
proper noun
solid; strong; firm
adherence; sticking (to); fixation
obstinate; stubborn; obdurate; headstrong; willful; perverse
somewhat hard; somewhat firm; fairly hard; on the hard side
firm; unshakeable; resolute
solidification
watching (esp. during an emergency); being on alert