Definitions for unsayʌnˈseɪ
Random House Webster's College Dictionary
to withdraw (something said), as if it had never been said; retract.
Origin of unsay:
swallow, take back, unsay, withdraw(verb)
take back what one has said
"He swallowed his words"
To withdraw, retract (something said).
To not have said (since this is physically impossible usually in the subjunctive, as I wish I could unsay).
to recant or recall, as what has been said; to refract; to take back again; to make as if not said