Marry one without trace of duplicity (5)
I believe the answer is:
unite
'marry' is the definition.
(I've seen this before)
'one without trace of duplicity' is the wordplay.
I cannot quite see how this works, but
'one' could be 'un' (northern English dialect form of 'one') and 'un' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for unite that I've seen before include "Join together, become allies" , "ally" , "old coin" , "Couple" , "Group of workers" .)