Junior masonic centre (3)
I believe the answer is:
son
'junior' is the definition.
(I've seen this in another clue)
'masonic centre' is the wordplay.
'centre' says to take the centre.
The middle of 'masonic' is 'SON'.
(Other definitions for son that I've seen before include "Heir" , "A relative" , "Native" , "Young boy" , "Male descendant" .)