From Longman Dictionary of Contemporary Englishfirst offenderˌfirst ofˈfender noun [countable] SCCsomeone who is guilty of breaking the law for the first time
Examples from the Corpus
first offender• Defending, Robert Fairbairn, said his client, a first offender, was very ashamed of what she had done.• Hayman, a first offender, was sent to a young offenders institution for three years. 