WordNet (r) 3.0 (2006):

decriminalise
    v 1: make legal; "Marijuana should be legalized" [syn:
         legalize, legalise, decriminalize, decriminalise,
         legitimize, legitimise, legitimate, legitimatize,
         legitimatise] [ant: criminalise, criminalize,
         illegalise, illegalize, outlaw]