Uncle Arthur's day off? It isn't apparent (7)
I believe the answer is:
unclear
'uncle arthur's day off? it isn't apparent' is the definition.
I can't judge whether this definition defines the answer.
'uncle arthur's day off?' is the wordplay.
'arthur's day off?' becomes 'Ar' ('Arthurs' with 'thurs', a day, taken off).
'uncle'+'ar'='UNCLEAR'
Can you help me to learn more?
(Other definitions for unclear that I've seen before include "Not easy to see or understand" , "Imprecise, hazy" , "hard to understand" , "An ulcer (anag)" , "Cloudy or opaque" .)