silentious
Habitually taciturn; prone to silence.
Yet Will had very good qualities too: gentle, tractable, and, above all, grateful; silentious, even to a fault: he spoke, at any time, very little, but made it up emphatically with action;
Where it comes from
Borrowed from Latin silentiōsus. By surface analysis, silence + -ous.
Adapted from the Wiktionary entry silentious (CC BY-SA 4.0).