The Collaborative International Dictionary
Ex post facto \Ex" post` fac"to\, or ||Ex postfacto \Ex" post`fac"to\ ([e^]ks" p[=o]st" f[a^]k"t[-o]). [L., from what is done afterwards.] (Law) From or by an after act, or thing done afterward; in consequence of a subsequent act; retrospective.
Ex post facto law, a law which operates by after enactment.
The phrase is popularly applied to any law, civil or
criminal, which is enacted with a retrospective effect,
and with intention to produce that effect; but in its true
application, as employed in American law, it relates only
to crimes, and signifies a law which retroacts, by way of
criminal punishment, upon that which was not a crime
before its passage, or which raises the grade of an
offense, or renders an act punishable in a more severe
manner that it was when committed. Ex post facto laws are
held to be contrary to the fundamental principles of a
free government, and the States are prohibited from
passing such laws by the Constitution of the United
States.
--Burrill.
--Kent.
Usage examples of "ex postfacto".
For that matter, I wasn't sure whether he was speaking only of what the psychological effect on them might be-or whether he was himself convinced that Hector Cameron ought to be capable of dealing with this ex postfacto threat to his wife and plantation.