Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

mortĭfer or (rarely) mortĭfĕrus, ĕra, ĕrum, adj. [mors-fero], death-bringing, death-dealing, deadly, fatal (class.; syn.: lethalis, funestus): poculum, Cic. Tusc. 1, 29, 71: morbus, id. Div. 1, 30, 63: vulnus, id. Leg. 2, 5, 13: bellum, Verg. A. 6, 279: gravior dolor nec tamen mortiferus, Cels. 4, 2 init.; 5, 26, 22; Aug. de Util. Cred. § 36: res mortifera est inimicus pumice levis, Juv. 9, 95; 10, 10.
Neutr. plur. as subst.: mortĭfĕra, um, deadly things: cur tam multa mortifera terra mortique (deus) disperserit, Cic. Ac. 2, 38, 120 (B. and K. pestifera).
Hence, adv.: mortĭfĕrē, mortally, fatally (post-Aug.): mortifere aegrotare, Plin. Ep. 3, 16, 3: vulnerare, Dig. 9, 2, 36, § 1.