Member of the reformed Order of Cistercians of the Strict Observance noted for their rule of silence (8)
I believe the answer is:
trappist
(Other definitions for trappist that I've seen before include "Monk vowed to silence" , "Order (of monks) noted for vow of silence" , "who likes to be silent?" , "Austere (and silent) monk" , "Past trip (anag.)" .)