Lewis & Short

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.