Rank mouth (5)
I believe the answer is:
utter
I believe this is a double definition.
'rank' is the first definition.
(synonyms)
'mouth' is the second definition.
(I know that mouth is a more specific form of belie)
(Other definitions for utter that I've seen before include "Total - speak" , "Positive" , "Circulate" , "Complete madman" , "Put into words" .)