Taciturn
Etymology
From Latin taciturnus, "not talkative," built on tacēre, "to be silent" (also the root of "tacit"). It entered English in the eighteenth century already describing a fixed disposition rather than a passing silence. The sense has stayed remarkably stable: a person, or a temperament, that keeps its own counsel.
adjective · /TAS-ih-turn/
Habitually saying very little; reserved and sparing in speech.
What it names
The settled, temperamental quietness of a person who is silent by nature, not because of any particular mood or occasion.
Example
Her grandfather was a taciturn man who could sit through an entire meal and offer nothing but a nod.
Related idea
Reticent is about a specific reluctance to speak, often on a particular subject; taciturn is a permanent trait of the personality.