undĕcĭmus, a, um, num. adj. [unusdecimus],
the eleventh : legio, Liv. 30, 18, 10: annus, Verg. E. 8, 39: dies, Plin. 11, 54, 118, § 283.
ūndecimus adj. num. unus+decimus, the eleventh : hora: legio, L.: annus, V. ...
An Elementary Latin Dictionary