Synonyms for Block off:

n.

discourage, avert, prohibit, avoid, prevent, knock something on the head, get in the way of something, squash. seal, shut, lock out, bolt, jam something open/shut, fasten. block off (noun)
close off, shut off, blockade.

v.

competition (verb)
blockade.
contact (verb)
close off, shut off.
enclose (verb)
blockade.
isolate (verb)
close off.

Other synonyms:

fasten. lock out, seal. shut. bolt.