Vague relative has a right (7)
I believe the answer is:
unclear
'vague' is the definition.
(similar in meaning)
'relative has a right' is the wordplay.
'relative' becomes 'uncle' (uncle is a kind of relative).
'has' means one lot of letters go next to another.
'a right' becomes 'ar' (I've seen this in other clues).
'uncle'+'ar'='UNCLEAR'
(Other definitions for unclear that I've seen before include "Ill-defined or not easily understood" , "Poorly described" , "Not obvious, obscure" , "Doubtful" , "Not easy to grasp" .)