IPA: /ˌdiːˈkrɪmɪnaɪz/
KK: /diˈkrɪmɪnəˌlaɪz/
To make an action or behavior no longer considered a crime, often by changing the law.
The government decided to decriminalize the use of marijuana in the state.
Past: decriminalized
Past Participle: decriminalized
Decriminalize is formed from "de-" (meaning down or away) and "criminalis" (from Latin, meaning relating to crime) and "-ize" (a suffix used to form verbs meaning to make or to become). The word means to remove the criminal status from an act, effectively making it no longer a crime.
Think of 'removing' ('de-') the 'criminal' status ('criminalis') from an action — that's what decriminalize means.