Helicopter swiftly circling hospital (6)
I believe the answer is:
apache
'helicopter' is the definition.
(US army helicopter)
'swiftly circling hospital' is the wordplay.
'swiftly' becomes 'apace' ('apace' can be a synonym of 'quickly').
'circling' is an insertion indicator (circling can mean going around or containing).
'hospital' becomes 'h'.
'apace' placed around 'h' is 'APACHE'.
(Other definitions for apache that I've seen before include "N. American native; French ruffian" , "North American native tribe" , "Geronimo was of this native American tribe" , "American Indian of New Mexico and Arizona" , "nickname of US State" .)