Doctor in a different channel (5)
I believe the answer is:
drain
'channel' is the definition.
(drain is a kind of channel)
'doctor in a different' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor'**).
'different' indicates an anagram.
'in'+'a'='ina'
'ina' anagrammed gives 'ain'.
'dr'+'ain'='DRAIN'
(Other definitions for drain that I've seen before include "Deprive of vitality" , "Siphon off" , "Deprive gradually of strength or resources" , "Culvert" , "Waste channel/pipe" .)