shut vs seal off

shut is an adjective but seal off is not an adjective.

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

As verbs, seal off is a hyponym of shut; that is, seal off is a word with a more specific, narrower meaning than shut:

Other hyponyms of shut include snap, slat, bang, slam, shutter, draw, roll up, bung, seal.

shut (adjective)	seal off (adjective)
not open
used especially of mouth or eyes

shut (verb)	seal off (verb)
move so that an opening or passage is obstructed; make shut	impose a blockade on
become closed	make tight; secure against leakage
prevent from entering; shut out