Centre identified by married man dropping by (3)
I believe the answer is:
hub
'centre' is the definition.
(hub is a kind of centre)
'married man dropping by' is the wordplay.
'married man' becomes 'hubby' (synonyms).
'dropping' indicates named letters should be taken away.
'hubby' with 'by' removed is 'HUB'.
'identified by' acts as a link.
(Other definitions for hub that I've seen before include "Nave of a wheel" , "Centre of activity" , "Central part of a car wheel" , "Centre (of network)" , "Centre of wheel" .)