Uniform has got carried outside boundary (6)
I believe the answer is:
bourne
'boundary' is the definition.
(bourne is a kind of boundary)
'uniform has got carried outside' is the wordplay.
I cannot really see how this works, but
'uniform' could be 'u' (phonetic alphabet: alpha, bravo, charlie etc.) and 'u' is found in the answer.
'carried' could be 'borne' (I've seen this before) and 'borne' is found in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
(Other definitions for bourne that I've seen before include "goal" , "Stream" .)