What does onus mean?
Onus is a formal noun meaning a responsibility, obligation, or burden that falls on a particular person or party. It is especially common in legal and administrative contexts, where it identifies who must satisfy a requirement or prove a case. It often appears in constructions that place the onus on someone: this may describe a duty created by law, contract, evidence, or custom rather than a voluntary task. The word is more precise than duty because it emphasizes the load of responsibility that must be carried, and it can sound formal or judicial without being archaic. Although now most familiar from legal writing, onus derives from a Latin word meaning burden or load and retains that physical metaphor in abstract uses. Recognising it helps readers identify subtle shifts in responsibility, particularly when a text distinguishes one party’s evidentiary burden from another’s. It is therefore useful in contracts, judgments, policies, and formal debate.
nounA responsibility, obligation, or burden that falls on a particular person or party, especially a burden of proof that must be discharged.
- A responsibility, obligation, or burden falling on a particular person or party.
- The burden of proving a claim or fact, especially in legal proceedings.
"The onus of proving that the goods were defective lies with the manufacturer."
"It is the duty of the prosecution to establish that the defendant is guilty."
"The shift to remote working has placed a new onus on managers to maintain team cohesion."
Onuses is the ordinary English plural; onera is also used as a learned or legal variant.
"The judgment considered the respective onuses of proof allocated to the parties."
Onus is Latin for “load,” and legal English still uses it as one.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does onus come from?
Onus entered English in the early 17th century from Latin ōnus, meaning “burden” or “load.” Latin formed onerosus from the same root, the source of English onerous and its derivatives, while Greek had the cognate onos, also meaning “burden.” In modern English, the word developed from the general idea of a load into the more abstract sense of responsibility or obligation.
Related word forms
How onus is actually used
Formal and often legalistic, but standard in British and US English. It is usually neutral, although contexts involving proof, liability, or compliance can sound adversarial because the term identifies who must bear responsibility.