... because R before end of June is genuine (7)
I believe the answer is:
sincere
'genuine' is the definition.
(synonyms)
'because r before end of june' is the wordplay.
'because' becomes 'since' (I've seen this before).
'before' means one lot of letters go next to another.
'end of june' becomes 'e' (I've seen this in other clues).
'since'+'r'+'e'='SINCERE'
'is' acts as a link.
(Other definitions for sincere that I've seen before include "Unaffected" , "Pure" , "Unfeigned, genuine" , "Honest, frank" , "Free from deceit" .)