shut up
噤 centers on closing the mouth tightly: to shut up or keep silent.
噤 combines 口 (mouth) with 禁 (prohibition), suggesting a mouth that is prohibited from speaking. The exact historical development is uncertain, but the component relationship is clear.
The mouth 口 is under a prohibition 禁: imagine a mouth clamped shut by a forbidden sign, forced to shut up.
For キン, picture a king silencing his subjects with a stern look: king -> キン, and the mouth shuts up.
to shut one's mouth; to hold one's tongue; to keep silent