Understood to be silent (5)
I believe the answer is:
tacit
I believe this clue is a double definition.
'understood' is the first definition.
(I've seen this before)
'silent' is the second definition.
(synonyms)
'to be' is the link.
(Other definitions for tacit that I've seen before include "Wordless" , "without speaking" , "Silent - understood" , "Not said though understood" , "Understood, not spoken or played" .)