Conjugal art confused with mail (7)
I believe the answer is:
marital
'conjugal' is the definition.
(I've seen this in another clue)
'art confused with mail' is the wordplay.
'confused with' is an anagram indicator.
'art' anagrammed with 'mail' can make 'MARITAL'.
(Other definitions for marital that I've seen before include "related to union" , "Referring to a union" , "describing matrimony" , "Relating to wedded life" , "Of the nature of marriage" .)