Lewis Short
trīga (noun F) : contr. from trijuga. *
* A team of three horses, or a chariot drawn by three horses, Dig. 21, 1, 38, § 14.
* A set of three, a triad, three, Arn. 4, 136; cf. Anthol. Lat. 1, p. 439.
Charlton T. Lewis, Charles Short, A Latin Dictionary