Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
un-dēni, ae, a, num. distrib. adj. [unus], eleven each, eleven distributively: pariuntur undeni, Plin. 11, 25, 30, § 91: cubitis, id. 36, 8, 14, § 65 Sillig N. cr.: Musa per undenos emodulanda pedes, i. e. with a hexameter and pentameter, elegiac verse, Ov. Am. 1, 1, 30: me quater undenos sciat implevisse Decembres, i. e. forty-four years, Hor. Ep. 1, 20, 27.
In sing.: bisque undena pars, Manil. 4, 451.