Doctor to admit to flood (5)
I believe the answer is:
drown
'flood' is the definition.
(I've seen this before)
'doctor to admit' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'to admit' becomes 'own' (own can mean to admit or acknowledge).
'dr'+'own'='DROWN'
'to' acts as a link.
(Other definitions for drown that I've seen before include "Perish in water" , "Flood (an area)" , "Die in sea" , "Completely conceal" , "Sink" .)