gatehouse

As nouns the difference between gatehouse and portcullis

is that gatehouse is a lodge besides the entrance to an estate; often the residence of a gatekeeper; also a dwelling formerly used as such a residence while portcullis is a gate in the form of a grating which is lowered into place at the entrance to a castle, fort, etc.

As a verb portcullis is

to obstruct with, or as with, a portcullis; to shut; to bar.

As nouns the difference between barbican and gatehouse

is that barbican is a tower at the entrance to a castle or fortified town while gatehouse is a lodge besides the entrance to an estate; often the residence of a gatekeeper; also a dwelling formerly used as such a residence.