silent

1. Marked by absence of noise or sound; still.

2. Not inclined to speak; not talkative.

3. Unable to speak.

4. Refraining from speech: Do be silent.

5. Not voiced or expressed; unspoken: a silent curse; silent consent.

6. Inactive; quiescent: a silent volcano.

7. Linguistics Having no phonetic value; unpronounced: the silent b in subtle.

8. Having no spoken dialogue and usually no soundtrack. Used of a film.

9. Producing no detectable signs or symptoms: a silent heart attack.

Synonyms: These adjectives describe people who are sparing with speech. Silent often implies a habitual disinclination to speak or to speak out: "The coroner was a very silent man" (Mary Roberts Rinehart).
The term may also mean refraining from speech, as out of fear or confusion: "The person in custody must, prior to interrogation, be clearly informed that he has the right to remain silent" (Earl Warren).
Reticent suggests a reluctance to share one's thoughts and feelings: "She had been shy and reticent with me, and now . . . she was telling me aloud the secrets of her inmost heart" (W.H. Hudson).
Reserved suggests aloofness and reticence: "a reserved man, whose inner life was intense and sufficient to him" (Arnold Bennett).
Taciturn implies unsociableness and a tendency to speak only when it is absolutely necessary: "At the Council board he was taciturn; and in the House of Lords he never opened his lips" (Thomas Macaulay).
Laconic denotes terseness or conciseness in expression, but when applied to people it often implies an unwillingness to use words: "Mountain dwellers and mountain lovers are a laconic tribe. They know the futility of words" (Edna Ferber).
Secretive implies a lack of openness about or even concealment of matters that could in all conscience be discussed: was secretive about my vacation plans.
Uncommunicative suggests a disposition to withhold opinions, feelings, or knowledge from others: an uncommunicative witness.
Tightlipped strongly implies a steadfast unwillingness to divulge information being sought: remained tightlipped when asked about her personal life. See Also Synonyms at still¹.