Onus Definition: Latin: the burden. Related Terms: Burden of Proof It is usually used in the context of evidence. The onus of proof in criminal cases lies with the government. It is the government that has the burden of proving beyond reasonable doubt. In civil cases, the onus of proof lies with the plaintiff who must prove his case by balance of probabilities. Thus onus refers both to the party with the burden, and to the scope of that burden, the latter depending whether the context is criminal or civil. French: fardeau. REFERENCES: Duhaime, Lloyd, Legal Definition of Burden of Proof Categories & Topics: Civil Litigation & Evidence Law Dictionary Criminal Law Dictionary Dictionary of Latin Law Terms Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!