from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
SPECIAL NON EST FACTUM. The name of a plea by which the defendant says that
the deed which he has executed is not his own or binding upon him, because
of some circumstance which shows that it was not intended to be his deed, or
because it was not binding upon him for some lawful reason; as, when the
defendant delivered the deed to a third person as an escrow to be delivered
upon a condition, and it has been delivered without the performance of the
condition, he may plead non est factum, state the fact, of the conditional
delivery, the non-performance of the condition, and add, "and so it is not
his deed;" or if the defendant be a feme covert, she may plead non est
factum, that she was a feme covert at the time the deed was made, "and so it
is not her deed." Bac. Ab. Pleas, &c. H 3, 1 2; Gould. on Pl. c. 6, part 1,
Sec. 64. See Issint.