Married? He's silly to get engaged! (4)
I believe the answer is:
mesh
'get engaged' is the definition.
(I've seen this before)
'married? he's silly' is the wordplay.
'married?' becomes 'm'.
'silly' indicates an anagram.
'hes' with letters rearranged gives 'esh'.
'm'+'esh'='MESH'
'to' acts as a link.
(Other definitions for mesh that I've seen before include "Interlaced structure" , "Web" , "Get in harmony with" , "Get engaged" , "Lattice" .)