mut- (silent)

(Greek > Latin: unable to speak, inarticulate, dumb; uttering no sound, silent, still, quiet)

Cave tibi cane muto, aqua silente.
Beware of the silent dog and still water.

A Latin idiom: "Stagnant water can poison you." "Silent dogs can bite." Some Romans believed that taciturn adversaries were more dangerous than the ones who made a lot of noise.

mute
1. Refraining from producing speech or vocal sounds.
2. Unable to speak or to vocalize, as certain animals.
3. Linguistics: Not pronounced, silent, as the e in the word house and mute.
4. Someone who is incapable of speech; not making any sound; silent; usually because of deafness, loss of or damage to the tongue, etc.
5. To soften the tone, color, shade, or hue of.
6. A clip pad, or other device, used to soften, deaden, or muffle the sound of a musical instrument.
muted, muting, mutes
1. To soften or muffle the sound of.
2. To soften the tone, color, shade, or hue of.
muteness
A reference to people who are unable to speak; being mute or deaf-mute.
mutism
1. The inability to speak.
2. A refusal to speak either at all times or on specific occasions, which may indicate trauma or stress.
selective mutism (SM)
Seemingly incongruous behavior in which someone exhibits a ready flow of speech in private, but silence in public.

Silence words. More silence-content words at these links: silen- and tacit-.