taciturn
adjective·/ˈtæs.ɪ.tɝːn/
Habitually silent and sparing in speech, often from temperament rather than mere circumstance. A taciturn person has a guarded interior, speech withheld rather than simply minimized.
He was taciturn at parties, smiling as if conversation were a language he understood but didn’t need.
Etymology
From Latin taciturnus, from tacere “to be silent.” A small verb becomes a character trait.
Related Words
reticentreserved; sometimes merely cautious
laconicbrief, often pointed
mutesilent, sometimes by inability
insouciantcan mimic taciturnity, for different reasons