Excellent tour taking in base (11)
I believe the answer is:
outstanding
'excellent' is the definition.
(thesaurus)
'tour taking in base' is the wordplay.
'tour' becomes 'outing' (an outing is a tour or trip).
'taking in' means one lot of letters goes inside another.
'base' becomes 'stand' (synonyms).
'outing' placed around 'stand' is 'OUTSTANDING'.
(Other definitions for outstanding that I've seen before include "in relief?" , "Superb" , "brilliant" , "Not paid yet" , "Exceptionally good" .)