De*fea"sance (?), n. [OF.
defesance, fr. defesant, F. défaisant, p.
pr. of defaire, F. défaire, to undo. See
Defeat.] 1. A defeat; an overthrow.
After his foes' defeasance.
2. A rendering null or void.
3. (Law) A condition, relating to a
deed, which being performed, the deed is defeated or rendered void;
or a collateral deed, made at the same time with a feoffment, or
other conveyance, containing conditions, on the performance of which
the estate then created may be defeated.
&fist; Mortgages were usually made in this manner in former times,
but the modern practice is to include the conveyance and the
defeasance in the same deed.