Mounties oddly silent (4)
I believe the answer is:
mute
'silent' is the definition.
('mute' can be a synonym of 'silent')
'mounties oddly' is the wordplay.
'oddly' means one should take alternating letters.
The alternate letters of 'mounties' are 'MUTE'.
(Other definitions for mute that I've seen before include "Silence" , "Device that softens the tone of a musical instrument" , "Speechless, soundless" , "Device for softening musical sound" , "Silent, refraining from speaking" .)