One who gives name in entrance (5)
I believe the answer is:
donor
'one who gives' is the definition.
(I've seen this before)
'name in entrance' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'in' indicates putting letters inside.
'entrance' becomes 'door' (door is a kind of entrance).
'n' inserted inside 'door' is 'DONOR'.
(Other definitions for donor that I've seen before include "A giver, often of blood" , "One contributing" , "Generous type" , "Giver, of blood say" , "Maker of gift" .)