Particular art nice, surprisingly (7)
I believe the answer is:
certain
'particular' is the definition.
(I know that particular can be written as certain)
'art nice surprisingly' is the wordplay.
'surprisingly' indicates anagramming the letters (a surprising ordering of the letters).
'art'+'nice'='artnice'
'artnice' with letters rearranged gives 'CERTAIN'.
(Other definitions for certain that I've seen before include "Sure, definite" , "Unquestionable" , "Known beyond doubt" , "Convinced" , "bound" .)