Latin-Roman Numeral Words: unus to M (mille)Numbers (Latin: Roman numerals, cardinals followed by ordinals).Numbers are the common denominator of everyday life, as essential to modern society as language.
 
1, I  
unus (unus [masculine], una [feminine], unum [neuter]): one; primus (prima, primum), first. 
diurnal: Happening once a day.
 
annual: Happening once a year.
 
2, II  
duo (duae, duo): two; secundus (secunda, secundum), second. There are no gender distinctions after II (two), except when such are indicated as with 200 through 900 and some of the ordinals. 
semidiurnal: Happening twice a day.
 
biannual: Happening twice a year.
 
biennial: Happening every second year.
 
biweekly: Happening twice a week or every two weeks.
 
semiweekly: Happening twice a week.
 
semimonthly: Happening twice a month.
 
bimonthly: Happening twice a month or once every two months.
 
biyearly: Happening twice a year or every two years.
 
semiannual: Happening twice a year.
 
3, III 
tres (tria): three; tertius (tertia, tertium), third. 
triweekly: Happening three times a week or every three weeks.
 
4, IV, IIII 
quattuor: four; quartus (quarta, quartum), fourth.
 
quadrennial: Happening once in four years.
 
5, V 
quinque: five; quintus (quinta, quintum), fifth.
 
quinquennial: The fifth anniversary.
 
6, VI 
sex: six; sextus (sexta, sextum), sixth.
 
sexennial: The sixth anniversary.
 
7, VII 
septem: seven; septimus (septima, septimum), seventh.
 
septennial: The seventh anniversary.
 
8, VIII 
octo: eight; octavus (octava, octavum), eighth.
 
octennial: The eighth anniversary.
 
9, IX, VIIII 
novem: nine; nonus (nona, nonum), ninth.
 
novennial: The ninth anniversary.
 
10, X 
decem: ten; decimus/decumus (decima, decimum), tenth.
 
decennial: The tenth anniversary.
 
11, XI 
undecim: eleven; undecimus, eleventh.
 
12,  XII 
duodecim: twelve; duodecimus, twelfth.
 
13,  XIII 
tredecim: thirteen; tertius decimus, thirteenth.
 
14, XIV, XIIII 
quattourdecim: fourteen; quartus decimus, fourteenth.
 
15, XV 
quindecim: fifteen; quintus decimus, fifteenth.
 
16, XVI 
sedecim: sixteen; sextus decimus, sixteenth.
 
17, XVII 
septemdecim: seventeen; septimus decimus, seventeenth.
 
18, XVIII 
duodeviginti, octodecim: eighteen; duodevicesimus,
 
octavusdecimus, eighteenth. 19, XIX, XVIIII 
undeviginti, novemdecim: nineteen; undevicesimus,
 
novemdecimus, nineteenth. 20, XX 
viginti: twenty; vicesimus, twentieth.
 
vicennial: The twentieth anniversary.
 
21, XXI 
viginti unus, unus et viginti: twenty-one; unetvicesimus,
 
vicesimus primus, twenty-first. 22, XXII 
duoetviginti: twenty-two; duoetvicesimus, twenty-second.
 
28, XXVIII 
duodetriginta: twenty-eight; duodetricesimus, twenty-eighth.
 
29, XXIX, XXVIIII 
undetriginta: twenty-nine; undetricesimus, twenty-nineth.
 
30, XXX 
triginta: thirty; tricesimus, thirtieth.
 
38, XXXVIII 
duodequadraginta: thirty-eight;
 
duodequadragesimus, thirty-eighth. 39, XXXIX, XXXVIIII 
undequadraginta: thirty-nine; undequadragesimus, thirty-ninth.
 
40, XL, XXXX 
quadraginta: forty; quadragesimus, fortieth.
 
48, XLVIII 
duodequinquaginta: forty-eight;  
duodequinquagesimus, forty-eighth. 49, XLIX, XLVIIII 
undequinquaginta: forty-nine; undequinquagesimus, forty-ninth.
 
50, L 
quinquaginta: fifty; quinquagesimus, fiftieth.
 
semicentennial: The fiftieth anniversary.
 
60, LX 
sexaginta: sixty; sexagesimus, sixtieth.
 
70, LXX 
septuaginta: seventy; septuagesimus, seventieth.
 
80, LXXX 
octoginta: eighty; octogesimus, eightieth.
 
90, XC, LXXXX 
nonaginta: ninety; nonagesimus, ninetieth.
 
100, C 
centum: one hundred; centesimus, hundredth.
 
centennial: The hundredth anniversary.
 
101, CI 
centum (et) unus: one hundred one; centesimus (et) primus, hundred first. 
sesquicentennial: The one-hundred fiftieth anniversary.
 
200, CC 
ducenti (ducentae, ducenta): two hundred; ducentesimus, two hundredth. 
bicentennial: The two-hundredth anniversary.
 
bisemicentennial: The two-hundred fiftieth anniversary.
 
300, CCC 
trecenti (trecentae, trecenta): three hundred; trecentesimus, three hundredth. 
tricentennial, tercentenary: The three-hundredth anniversary.
 
trisemicentennial, tersemicentennial: The three-hundred fiftieth anniversary.
 
400, CD, CCCC 
quadringenti (quadringentae, quadringenta): four hundred; quadringentesimus, four hundredth. 
quadricentennial: The four-hundredth anniversary.
 
quadrisemicentennial: The four-hundred fiftieth anniversary.
 
500, D 
quingenti (quingentae, quingenta): five hundred; quingentesimus, five hundredth. 
quincentennial: The five-hundredth anniversary.
 
quinsemicentennial: The five-hundred fiftieth anniversary.
 
600, DC 
sescenti (sescentae, sescenta): six hundred; sescentesimus, six hundredth. 
700, DCC 
septingenti (septingentae, septingenta): seven hundred; 
 
septingentesimus, seven hundredth. 800, DCCC 
octingenti (octingentae, octingenta): eight hundred; 
 
octingentesimus, eight hundredth. 900, CM, DCCCC 
nongenti (nongentae, nongenta): nine hundred; 
 
nongentesimus, nine hundredth. 1 000, M 
mille: one thousand; millesimus, one thousandth.
 
2 000, MM 
duo milia: two thousand; bis millesimus, two thousandth.
 
The origins of some of the Latin numerical symbols: 
V (5) is said to represent the hand with all five fingers spread apart. 
X (10) is formed by joining an inverted V to the bottom of the usual symbol V for five. 
L (50) represents the lower part of C (100) without the curve of the C. 
C (100) stands for the initial letter of centum. 
D (500) is a combination of L and a reversed C [the symbol meaning times ten or 50 times 10 = 500]. 
M (1 000) stands for the initial letter of mille. 
Source: Living Latin, A contemporary Approach, Book Two
 
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