Lewis & Short

tŭbĭlustrĭum or tŭbŭlustrĭum, ii, n. [tuba-lustro], a festival held on the 23d of March and 23d of May, when the trumpets used at sacrifices were purified, the feast of trumpets: dies tubulustrium appellatur, quod eo die in atrio sutorio sacrorum tubae lustrantur, Varr. L. L. 6, § 14 Müll. (cf. Ov. F. 3, 849).
Also plur.: tubilustria, Ov. F. 5, 725; cf. Fest. p. 352 Müll.