Dad’s brother has a right to be ambiguous! (7)
I believe the answer is:
unclear
'ambiguous' is the definition.
(similar in meaning)
'dad's brother has a right' is the wordplay.
'dad's brother' becomes 'uncle' (I've seen this in another clue).
'has' means one lot of letters go next to another.
'a right' becomes 'ar' (I've seen this in other clues).
'uncle'+'ar'='UNCLEAR'
'to be' is the link.
(Other definitions for unclear that I've seen before include "hard to understand" , "Vague" , "Cloudy or opaque" , "Not transparent or intelligible" , "Not easy to grasp" .)