These words are comparable when they are applied to persons or things that make no sound. Silent simply means refraining from speech or being without noise; it does not necessarily suggest serenity or motionlessness: His silent reproach was accompanied by vigorous gestures; a silent film; a silent conversation between deaf-and-dumb people who communicated by sign language. Because it implies only the absence of sound, silent can be more emphatic than any of the other words: The crowd fell silent at the news that the Prime Minister was dead.

Quiet and still , although denoting silence, have different implications. Quiet implies freedom from activity or commotion; still suggests an unruffled or tranquil state, and often implies that the calm is an interlude between periods of noise or agitation. In most contexts, therefore, silent , quiet and still are not interchangeable without changing the sense: a quiet street; a quiet neighbourhood; a still forest. Note that there is a sense of permanence about quiet but none about still , which indeed suggests the potentiality of the opposite of stillness: a still moment when they eye of the storm passed overhead. On the other hand, when referring simply to the absence of speech, and especially if used predicatively, the three words may be interchangeable: a child who keeps silent (or quiet or still ). Even here still is ambiguous, since it may simply suggest the absence of fidgeting.

Noiseless is used in commerce, usually to refer to machines that are inherently noisy, such as typewriters, air-conditioners and the like, in order to persuade consumers to purchase a particular brand that is supposed to be quieter than others. Like most advertising claims, it must be taken as a relative term, in this case meaning comparatively quiet . In more precise contexts noiseless means literally without any noise: the noiseless flight of an owl; the noiseless tread of a cat. In this sense it is synonymous with silent, which is also weakened in this way on occasions: What a silent engine this car has.