Join together and marry round end of April (4)
I believe the answer is:
weld
'join together' is the definition.
(I've seen this before)
'marry round end of april' is the wordplay.
'marry' becomes 'wed' ('wed' can be a synonym of 'marry'**).
'round' is an insertion indicator.
'end of' indicates one should take the final letters.
The last letter of 'april' is 'l'.
'wed' placed around 'l' is 'WELD'.
'and' acts as a link.
(Other definitions for weld that I've seen before include "Join using fusion" , "Join (metal) by melting" , "Join intimately together" , "Fuse metal parts" , "Bond" .)