Large British soldier gets turned (3)
I believe the answer is:
big
'large' is the definition.
(synonyms)
'british soldier gets turned' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in BBC).
'soldier' becomes 'gi' (term for US soldier).
'gets turned' is a reversal indicator.
'gi' written backwards gives 'ig'.
'b'+'ig'='BIG'
(Other definitions for big that I've seen before include "Of considerable size" , "Large or substantial" , "Huge" , "Circus tent" , "oversized" .)