vicesimus

Latin

**Latin numbers ^(edit)**
		200
← 10	^{[a], [b], [c], [d]} ← 19	XX 20	21 → ^{[a], [b]}	30 →
		2^{[a], [b]}
Cardinal: vīgintī Ordinal: vīcēsimus, vīgēsimus, vīcēnsimus, vīgēnsimus, vīcēnsumus Adverbial: vīciēs, vīciēns, vīgēsiēs Proportional: vīgecuplus, vīcecuplus, vigincuplus Distributive: vīcēnus, vīgēnus Fractional: vīcēsimus, vīgēsimus, vīcēnsimus, vīgēnsimus, vīcēnsumus

From the stem *vīcent- of vīgintī (“twenty”) before the replacement of /k/ with /ɡ/, ultimately from Proto-Indo-European *(d)widḱm̥ti(h₁). Particularly:

Remodeling of earlier *vīcēnssos, from Proto-Indo-European *widḱm̥t-tós (“twentieth”),^{[note 1]} with the added suffix of dec-imus.^[1]
Or, inherited from Proto-Italic *wīkenssamos, a direct continuation of Proto-Indo-European *widḱm̥t-tm̥Hós, containing the superlative suffix *-tm̥Hós (“-est”) (compare -issimus) as used also in Sanskrit विंशतिम (viṃśatima), विंशतितम (viṃśatitama, “twentieth”).^[2]

See also vīciēs and vīcēnus. Surface analysis vīgintī (“twenty”) +‎ -ēsimus (“-th”)

(Classical Latin) IPA^(key): /u̯iːˈkeː.si.mus/, [u̯iːˈkeːs̠ɪmʊs̠]
(modern Italianate Ecclesiastical) IPA^(key): /viˈt͡ʃe.si.mus/, [viˈt͡ʃɛːs̬imus]

vīcēsimus (feminine vīcēsima, neuter vīcēsimum); first/second-declension numeral

	masculine	feminine	neuter	masculine	feminine	neuter
	singular			plural
nominative	vīcēsimus	vīcēsima	vīcēsimum	vīcēsimī	vīcēsimae	vīcēsima
genitive	vīcēsimī	vīcēsimae	vīcēsimī	vīcēsimōrum	vīcēsimārum	vīcēsimōrum
dative	vīcēsimō	vīcēsimae	vīcēsimō	vīcēsimīs
accusative	vīcēsimum	vīcēsimam	vīcēsimum	vīcēsimōs	vīcēsimās	vīcēsima
ablative	vīcēsimō	vīcēsimā	vīcēsimō	vīcēsimīs
vocative	vīcēsime	vīcēsima	vīcēsimum	vīcēsimī	vīcēsimae	vīcēsima

^ The innovative use of *-tos to create ordinals and fractionals (“-th”) is found in several other branches of Indo-European. Sihler explains that it may have originated by metanalysis of *dḱm̥t-ós as *dḱm̥-tós, from which the *-t- was then applied analogically to other numerals. This was apparently early enough to trigger the dissimilatory rule *TT > *TˢT (>> Latin ss).

^ Sihler, Andrew L. (1995) New Comparative Grammar of Greek and Latin, Oxford, New York: Oxford University Press, →ISBN, § 399, page 433
^ De Vaan, Michiel (2008) “vīgintī”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 678