special contract vs sealed instrument

special contract and sealed instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
special contract	Yes	No	No	No
sealed instrument	Yes	No	No	No

As nouns, special contract and sealed instrument are synonyms defined as:

special contract and sealed instrument: a contract that is signed and has the (wax) seal of the signer attached

Other synonyms of special contract include contract under seal.

special contract (noun)	sealed instrument (noun)
a contract that is signed and has the (wax) seal of the signer attached	a contract that is signed and has the (wax) seal of the signer attached