Lewis & Short

1. būris, is, m. (būra, ae, f., Varr. R. R. 1, 19, 2) [acc. to Serv. ad Verg. G. 1, 170 (cf. also Isid. Orig. 20, 14, 2), contr. from βοῦς and οὐρά, ox-tail], the curved hinder part of the plough of the ancients, the plough-beam, Varr. ap. Serv. l. l.
Acc. burim, Verg. G. 1, 170 Serv. and Voss.; Varr. R. R. 1, 19, 2.