Conscious of fighting within hospital department (5)
I believe the answer is:
aware
'conscious of' is the definition.
(being conscious means being aware of something)
'fighting within hospital department' is the wordplay.
'fighting' becomes 'war'.
'within' is an insertion indicator.
'hospital department' becomes 'ae' (A and E, Accident and Emergency department).
'war' put inside 'ae' is 'AWARE'.
(Other definitions for aware that I've seen before include "Informed; conscious" , "Attentive" , "fly" , "Alert, conscious of" , "Conscious or having knowledge of" .)