seal off vs blockade

seal off is not a noun while blockade is a noun.

Word	Noun	Adjective	Verb	Adverb
seal off	No	No	Yes	No
blockade	Yes	No	Yes	No

As verbs, seal off and blockade are synonyms defined as:

seal off (noun)	blockade (noun)
	a war measure that isolates some area of importance to the enemy
	prevents access or progress

seal off (verb)	blockade (verb)
impose a blockade on	impose a blockade on
make tight; secure against leakage	obstruct access to
	render unsuitable for passage
	hinder or prevent the progress or accomplishment of