confinement, to tie
錮 centers on restricting movement or freedom: confining someone or tying something up so it cannot move freely.
錮 combines 金 (metal) with 固 (solid, firm), suggesting the idea of using metal to make something firm or immovable, hence confinement or tying.
Metal (金) that is solid and firm (固) can be used to confine or tie something securely. Imagine a metal chain or shackle that holds something in place.
For コ, picture a metal lock that is so solid it goes 'ko' when it snaps shut, confining whatever is inside.