Wide mouth contorted say: true (7)
I believe the answer is:
estuary
'wide mouth' is the definition.
'estuary' can be an answer for 'mouth' (I've seen this before). I'm not certain of the 'wide' bit.
'contorted say true' is the wordplay.
'contorted' indicates an anagram.
'say'+'true'='saytrue'
'saytrue' is an anagram of 'ESTUARY'.
Can you help me to learn more?
(Other definitions for estuary that I've seen before include "Here one comes close to the main" , "A surety for river mouth" , "Where tide meets stream" , "River near sea" , "a sort of English" .)