Lewis & Short

undēvīcēsĭmus or undēvīgēsĭ-mus, a, um, adj. [undeviginti], the nineteenth: anno undevicesimo post ejus mortem, Cic. Sen. 5, 14: expleto aetatis undevicesimo anno, Quint. 6, praef. § 4; Tac. A. 1, 45 (al. unetvicesimus): die undevigesimo, Col. 8, 5, 14.
The second and third syllable scanned short: senserat ire aquilas legio undevigesima, cujus, etc., Poët. ap. Anth. Lat. 2, p. 21.