Ziploc feature (4)
I believe the answer is:
seal
'ziploc feature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seal that I've seen before include "Mammal; impressed wax" , "Ratify" , "Sea beast - authenticating mark" , "Secure against leakage" , "Sea mammal in sale" .)