Professional meeting reported in March (10)
I believe the answer is:
procession
'march' is the definition.
(a procession of people marching)
'professional meeting reported in' is the wordplay.
'professional' becomes 'pro' (synonyms).
'meeting' becomes 'session' (session is a kind of meeting).
'reported in' shows a homophone (sound like) (reported can mean spoken).
'session' sounds like 'cession'.
'pro'+'cession'='PROCESSION'
(Other definitions for procession that I've seen before include "Parade, cavalcade" , "Motorcade" .)