ETYMOLOGY
from Latin taciturnus (taciturn) + -ous
EXAMPLE
“…The Legate was more taciturnous, and seldom entered into conversation with the Embassador, who, very prudently, forbore to ask questions about China in his presence…”
From: An Historical Account of the Embassy to the Emperor of China
By Earl George Macartney Macartney, 1797
Lexicophilia 