Radio-controlled aircraft, one used by medical practitioner (5)
I believe the answer is:
drone
'radio-controlled aircraft' is the definition.
('drone' can be a synonym of 'radio-controlled aircraft')
'one used by medical practitioner' is the wordplay.
'used by' says to put letters next to each other.
'medical practitioner' becomes 'dr' (Dr is an example).
'one' put after 'dr' is 'DRONE'.
(Other definitions for drone that I've seen before include "mollusc" , "Non-worker" , "Continuous low-pitched note" , "Continuous humming sound" , "Aeroplane" .)