adverb + (v.)toughen greatly, recently, unfortunately

(v.)toughen + adverb considerably

(v.)toughen + noun admission, border, code, course, embargo, enforcement, guideline, gun, immigration, language, law, meat, offender, penalty, policy, pollution, protein, provision, regulation, requirement, resolve, restriction, rhetoric, rule, safety, schedule, screening, skin, stance, standard  [See all][See only the most frequent]