Lewis & Short

tonsa, ae, f. [perh. from tundo], an oar (poet.; mostly in plur.; syn. remus).

        1. (α) Sing.: in mari magno tenere tonsam, Enn. ap. Fest. p. 356 Müll. (Sota, v. 3 Vahl. p. 164): valida tonsa, Val. Fl. 1, 369.
        2. (β) Plur., Enn. ap. Fest. p. 356 Müll. (Ann. v. 232; 235; 236 Vahl.); Lucr. 2, 554; Verg. A. 7, 28; 10, 299; Luc. 3, 527; 5, 448; Sil. 11, 492; Sen. Agam. 443 al.