The main point of connubial relations (3)
I believe the answer is:
nub
'the main point' is the definition.
(I've seen this before)
'of connubial relations' is the wordplay.
'of' indicates the answer is hidden within the clue.
'NUB' can be found hidden inside 'connubial relations'.
(Other definitions for nub that I've seen before include "Metal piece" , "'Gist, central idea (3)'" , "Small lump - main point" , "Crux; lump" , "Central point of bun" .)