Doctor with unit is a lazy person (5)
I believe the answer is:
drone
'lazy person' is the definition.
'doctor with unit' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor').
'with' says to put letters next to each other.
'unit' becomes 'one' ('one' can be a synonym of 'unit'**).
'dr'+'one'='DRONE'
'is a' acts as a link.
(Other definitions for drone that I've seen before include "Aeroplane" , "Talk boringly; a parasite" , "Speak long and tediously" , "Monotone" , "Continuous hum" .)