An effusive talk masking one's pain (7)
I believe the answer is:
anguish
'pain' is the definition.
(synonyms)
'an effusive talk masking one's' is the wordplay.
'effusive talk' becomes 'gush' (gushing is talking effusively).
'masking' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'gush' placed around 'i' is 'guish'.
'an'+'guish'='ANGUISH'
(Other definitions for anguish that I've seen before include "Great (mental) pain" , "Severe pain, physical or mental" , "Extreme torment" , "Great suffering" , "Hi, Angus - that hurts" .)