Charge hospital department with corrosion (7)
I believe the answer is:
entrust
'charge' is the definition.
(as in entrusting or charging someone with a task)
'hospital department with corrosion' is the wordplay.
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'with' says to put letters next to each other.
'corrosion' becomes 'rust' (rust is a kind of corrosion).
'ent'+'rust'='ENTRUST'
(Other definitions for entrust that I've seen before include "Commend" , "Invest, commit" , "Assign (a responsibility to someone)" , "Give custody of" , "Place in someone's 22 ac" .)