quieten

Concise Oxford English Dictionary © 2008 Oxford University Press:
quiet/ˈkwʌɪət/

▶adjective (quieter, quietest)

• 1 making little or no noise.

  ■ free from activity, disturbance, or excitement.

  ■ undisturbed; uninterrupted.

• 2 discreet, moderate, or restrained.

  ■ (of a person) tranquil and reserved.

  ■ (of a colour or garment) unobtrusive.

▶noun silence; calm. ▶verb chiefly N. Amer. make or become quiet.

– phrases
keep quiet refrain from speaking or revealing a secret.
keep something quiet keep something secret.
on the quiet informal secretly or unobtrusively.

– derivatives
quieten verb,
quietly adverb,
quietness noun.

– origin ME (as n. denoting peace as opposed to war): via OFr., based on L. quies, quiet- ‘repose, quiet’.