swallow vs unsay

swallow is a noun but unsay is not a noun.

Word	Noun	Adjective	Verb	Adverb
swallow	Yes	No	Yes	No
unsay	No	No	Yes	No

As verbs, swallow and unsay are synonyms defined as:

Other synonyms of swallow include take back, withdraw.

swallow (noun)	unsay (noun)
the act of swallowing
small long-winged songbird noted for swift graceful flight and the regularity of its migrations
a small amount of liquid food

swallow (verb)	unsay (verb)
believe or accept without questioning or challenge	take back what one has said
keep from expressing
tolerate or accommodate oneself to
take back what one has said
utter unclearly
engulf and destroy
pass through the esophagus as part of eating or drinking
enclose or envelop completely, as if by swallowing