Enthuse as Doctor John turns up (5)
I believe the answer is:
drool
'enthuse' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how one could define the other.
'doctor john turns up' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'john' becomes 'loo' (both can mean a toilet).
'turns up' says the letters should be written backwards.
'loo' written backwards gives 'ool'.
'dr'+'ool'='DROOL'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for drool that I've seen before include "Show excitement" , "Dogs may" , "Salivate" , "Slaver - drivel" , "dribble" .)