Sole tuba composition is complete (8)
I believe the answer is:
absolute
'is complete' is the definition.
(similar in meaning)
'sole tuba composition' is the wordplay.
'composition' indicates an anagram (letters arranged or composed in a different order).
'sole'+'tuba'='soletuba'
'soletuba' is an anagram of 'ABSOLUTE'.
(Other definitions for absolute that I've seen before include "Complete or not limited" , "Free from limits, power perhaps" , "unrestricted by constitutional checks" , "Unconditional, downright," , "Despotic" .)