ex post fac‧to law /ˌeks pəʊst ˈfæktəʊ ˌlɔː $ -poʊst ˈfæktoʊ ˌlɒː/ noun [countable] law
[Date: 1700-1800; Language: Latin; Origin: 'from a thing done afterward']
a law that makes a particular action into a crime, and then punishes people who took that action before it had legally become a crime

[TahlilGaran] Dictionary of Contemporary English ▲