WordNet sense 1 (hinder or prevent the progress or accomplishment of):

block, embarrass, hinder, obstruct, stymie, stymy, hinder

WordNet sense 2 (render unsuitable for passage):

bar, stop, barricade, block off, block up

WordNet sense 3 (impose a blockade on):

seal off

WordNet sense 4 (a war measure that isolates some area of importance to the enemy):

encirclement