silent

Concise Oxford English Dictionary © 2008 Oxford University Press:
silent/ˈsʌɪlənt/

▶adjective

• 1 not making or accompanied by any sound.

  ■ (of a film) without an accompanying soundtrack.

• 2 not speaking or not spoken aloud.

  ■ not prone to speak much.

• 3 (of a letter) written but not pronounced, e.g. b in doubt.

• 4 saying or recording nothing on a particular subject.

– derivatives
silently adverb.