【法】 溯及既往的法律

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.