special contract vs contract under seal

special contract and contract under seal both are nouns.

Word	Noun	Adjective	Verb	Adverb
special contract	Yes	No	No	No
contract under seal	Yes	No	No	No

As nouns, special contract and contract under seal are synonyms defined as:

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

Other synonyms of special contract include sealed instrument.

special contract (noun)	contract under seal (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