Meditation on mental topic perhaps (13)
I believe the answer is:
contemplation
'meditation' is the definition.
(synonyms)
'on mental topic perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'on'+'mental'+'topic'='onmentaltopic'
'onmentaltopic' is an anagram of 'CONTEMPLATION'.
(Other definitions for contemplation that I've seen before include "Deliberation" , "Reflective thought" , "Religious meditation" , "Cogitation" , "Survey" .)