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.

tŏnī̆trus, ūs, m., or tŏnī̆trŭum, ii (gen. tonitrui, Vulg. Marc. 3, 17), n. [tono], thunder.

        1. (α) Sing.: tonitrum auribus accipiamus, Lucr. 6, 164; 6, 171: tonitrum audire, Plin. 2, 54, 55, § 142: tonitruum terribile exsistit, id. 36, 13, 19, § 88; Sen. Q. N. 2, 54, 1; 2, 56, 1: auditum praeterea tonitruum, Treb. Gall. 5; Tert. adv. Marc. 3, 6: veri tonitrūs similitudinem imitari, Fest. s. v. Claudiana, p. 57 Müll.: caelum tonitru contremit, Poët. ap. Cic. de Or. 3, 39, 157: tonitru caelum omne ciebo, Verg. A. 4, 122: tonitruque tremescunt Ardua terrarum, id. ib. 5, 694.
          The nom. tonitru, neutr., rests solely on the authority of grammarians, Fest. s. v. pecuum, p. 246 Müll.; Serv. Verg. A. 5, 694; Charis. p. 18; 23; Prisc. p. 624; 685; 714 P. al.; v. Neue, Formenl. 1, 350 sq.
        2. (β) Plur. (form tonitra, Att. Trag. 480): tum fulgores et tonitrua exsistere, Cic. Div. 2, 19, 44; so, tonitrua, id. ib. 2, 18, 42; id. Phil. 5, 3, 8; Plin. 8, 47, 72, § 188; Ov. M. 1, 55; 12, 52; Juv. 5, 117: clamor tonitruum, Poët. ap. Cic. Fam. 8, 2, 1: subito coorta tempestas cum magno fragore tonitribusque, Liv. 1, 16; Plin. 2, 54, 55, § 145; 19, 3, 13, § 37; 37, 10, 55, § 150; Ov. M. 11, 496; Phaedr. 5, 7, 23 al.: tonitrubus, Aur. Vict. Orig. Gent. 14, 2; 20, 1: movere tonitrus, Ov. M. 2, 308: tonitrus agis, Stat. Th. 1, 258: imbres et tonitrus fieri derepente, Gell. 10, 12, 3.