The Collaborative International Dictionary
Onus probandi
Onus \O"nus\, n. [L.] A burden; an obligation.
Onus probandi[L.], obligation to furnish evidence to prove a thing; the burden of proof.
Wiktionary
onus probandi
n. (context legal English) the burden of proof, the onus; the duty of a party in a legal proceeding to prove an assertion of fact; it includes both the burden of production and the burden of persuasion.