obrussa, ae (pure Gr. collat. form = χρυσίον ὄβρυζον, obrȳzum aurum, Vulg. 2 Par. 3, 5; Isid. 16, 18, 2), f., = ὄβρυζον, the testing or assaying of gold by fire in a cupel (class.). Lit.: auri experimentum ignis est: id ipsum obrussam vocant, Plin. 33, 3, 19, § 59: aurum ad obrussam, refined, pure gold, Suet. Ner. 44.

— Trop., a test, touchstone, proof: adhibenda tamquam obrussa ratio, Cic. Brut. 74, 258: sic verus ille animus probatur: haec ejus obrussa est, this is its touchstone, its test, Sen. Ep. 13, 1: si omnia argumenta ad obrussam coeperimus exigere, to put to the proof, test accurately, id. Q. N. 4, 5, 1.