Corroded section of gate, at entrance (5)
I believe the answer is:
eaten
'corroded' is the definition.
(I've seen this before)
'section of gate at entrance' is the wordplay.
'section of' indicates the answer is hidden within the clue.
'EATEN' can be found hidden inside 'gate at entrance'.
(Other definitions for eaten that I've seen before include "Consumed" , "used for food" , "having been fed?" , "Put away" , "worried" .)