* Taciturn: Unwilling to speak; habitually silent.
* Reticent: Inclined to be silent or secretive; uncommunicative.
* Silent: Making no sound; not speaking.
* Quiet: Making little or no noise.
* Reserved: Slow to reveal emotion or opinions.
* Introverted: Shy and quiet; preferring to be alone.
* Mute: Unable to speak.
* Laconic: Using very few words; concise.
* Brief: Short in duration; concise.
* Succinct: Expressed in a few words; concise.
The best antonym depends on the specific context and nuance you want to convey.