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.

Source: Webster's Revised Unabridged Dictionary (1913)