What does ūndēnus mean in Latin?

ūndēnus, a numeral, means “eleven each; Eleventh.”.

How do you pronounce ūndēnus?

In classical Latin, [uːnˈdeː.nʊs]; in ecclesiastical (church) Latin, [unˈdɛː.nus].

numeralfirst/second-declension numeral

ūndēnus (feminine ūndēna, neuter ūndēnum)

Classical[uːnˈdeː.nʊs]Ecclesiastical[unˈdɛː.nus]

in pluralnumeraleleven each
Certus ūndēnōs deciēns per annōs orbis ut cantūs referatque lūdōs ter diē clārō totiēnsque grātā nocte frequentis.So when a hundred years and ten [literally, “ten times eleven”] bring round the cycle, game and song three days, three nights, shall charm again the festal throng.17 BCE, Horace, Carmen Saeculare
Mūsa per ūndēnōs ēmodulanda pedes!Muse, you must be measured through eleven feet.16 BCE, Ovidius, Amores 1.1.30
Medieval LatinnumeralpoeticEleventh.
Tauri nona mala est, similis cui tertia pars est post decimam nec non decimae pars septima iuncta; bisque undena notans et bis duodena nocentes quaeque decem trisque ingeminat fraudatque duobusc. 30 CE, Manilius, Astronomica 4.451

singular
form	masculine	feminine	neuter
nominative	ūndēnus	ūndēna	ūndēnum
genitive	ūndēnī	ūndēnae	ūndēnī
dative	ūndēnō	ūndēnae	ūndēnō
accusative	ūndēnum	ūndēnam	ūndēnum
ablative	ūndēnō	ūndēnā	ūndēnō
vocative	ūndēne	ūndēna	ūndēnum

plural
form	masculine	feminine	neuter
nominative	ūndēnī	ūndēnae	ūndēna
genitive	ūndēnum ūndēnōrum	ūndēnum ūndēnārum	ūndēnum ūndēnōrum
dative	ūndēnīs	ūndēnīs	ūndēnīs
accusative	ūndēnōs	ūndēnās	ūndēna
ablative	ūndēnīs	ūndēnīs	ūndēnīs
vocative	ūndēnī	ūndēnae	ūndēna

See dēnus. Equivalent to ūndecim + -nus.