<P> Roman fractions were based on a duodecimal system . From ​ ⁄ to ​ ⁄ they were expressed as multiples of twelfths (uncia "twelfth"; the source of the English words inch and ounce) and from ​ ⁄ to ​ ⁄ they were expressed as multiple twelfths less than the next whole unit--i.e. a whole unit less ​ ⁄, ​ ⁄ or ​ ⁄ respectively . There were also special terms for quarter (quadrans), half (semis), and three - quarters (dodrans). Dodrans is a Latin contraction of de-quadrans which means "a whole unit less a quarter" (de means "from"; quadrans means "quarter". Thus for the example of 175 years, the term is a quarter century less than the next whole (bi) century or 175 = (− 25 + 200). </P> <P> In Latin, it seems that this rule did not apply precisely for 11⁄2 . While secundus is Latin for "second", and bis for "twice", these terms are not used such as in sesqui - secundus . Instead sesqui (or ses) is used by itself . </P> <Table> <Tr> <Th> Anniversary </Th> <Th> Latin - derived term </Th> <Th> Other terms </Th> <Th> Comments </Th> </Tr> <Tr> <Td> 1⁄2 yearly </Td> <Td> Semiannual </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> 1 year </Td> <Td> Annual </Td> <Td> Paper </Td> <Td> </Td> </Tr> <Tr> <Td> 2 years </Td> <Td> Biennial </Td> <Td> Cotton </Td> <Td> </Td> </Tr> <Tr> <Td> 3 years </Td> <Td> Triennial </Td> <Td> Leather </Td> <Td> </Td> </Tr> <Tr> <Td> 4 years </Td> <Td> Quadrennial </Td> <Td> Linen </Td> <Td> </Td> </Tr> <Tr> <Td> 5 years </Td> <Td> Quinquennial </Td> <Td> Wood </Td> <Td> </Td> </Tr> <Tr> <Td> 6 years </Td> <Td> Sexennial </Td> <Td> Iron </Td> <Td> </Td> </Tr> <Tr> <Td> 7 years </Td> <Td> Septennial </Td> <Td> Wool </Td> <Td> </Td> </Tr> <Tr> <Td> 8 years </Td> <Td> Octennial </Td> <Td> Bronze </Td> <Td> </Td> </Tr> <Tr> <Td> 9 years </Td> <Td> Novennial </Td> <Td> Copper </Td> <Td> </Td> </Tr> <Tr> <Td> 10 years </Td> <Td> Decennial </Td> <Td> Tin / Aluminium </Td> <Td> </Td> </Tr> <Tr> <Td> 11 years </Td> <Td> Undecennial </Td> <Td> Steel </Td> <Td> </Td> </Tr> <Tr> <Td> 12 years </Td> <Td> Duodecennial </Td> <Td> Silk </Td> <Td> </Td> </Tr> <Tr> <Td> 13 years </Td> <Td> Tredecennial </Td> <Td> Lace </Td> <Td> </Td> </Tr> <Tr> <Td> 14 years </Td> <Td> Quattuordecennial </Td> <Td> Ivory </Td> <Td> </Td> </Tr> <Tr> <Td> 15 years </Td> <Td> Quindecennial </Td> <Td> Crystal </Td> <Td> </Td> </Tr> <Tr> <Td> 20 years </Td> <Td> Vigintennial / Vicennial </Td> <Td> China / Porcelain </Td> <Td> </Td> </Tr> <Tr> <Td> 25 years </Td> <Td> Quadranscentennial </Td> <Td> Silver jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 40 years </Td> <Td> Quadragennial </Td> <Td> Ruby jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 50 years </Td> <Td> Semicentennial / Quinquagenary </Td> <Td> Golden jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 60 years </Td> <Td> Sexagennial / Sexagenary </Td> <Td> Diamond jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 65 years </Td> <Td> </Td> <Td> Sapphire jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 70 years </Td> <Td> Septuagennial </Td> <Td> Platinum jubilee </Td> <Td> </Td> </Tr> <Tr> <Td> 100 years </Td> <Td> Centennial </Td> <Td> Centenary </Td> <Td> </Td> </Tr> <Tr> <Td> 125 years </Td> <Td> Quasquicentennial </Td> <Td> </Td> <Td> Term is broken down as quasqui - (and a quarter) centennial (100 years). Quasqui is a contraction from quadrans "a quarter" plus the clitic conjunction - que "and". The term was coined by Funk and Wagnalls editor Robert L. Chapman in 1961 . </Td> </Tr> <Tr> <Td> 150 years </Td> <Td> Sesquicentennial </Td> <Td> </Td> <Td> Term broken down as sesqui - (one and a half) centennial (100 years) </Td> </Tr> <Tr> <Td> 175 years </Td> <Td> Dodransbicentennial </Td> <Td> </Td> <Td> Dodrans is a Latin contraction of de-quadrans which means "a whole unit less a quarter" (de means "from"; quadrans means "quarter"). 175 years is a quarter century less than the next whole (bi) century or 175 = (− 25 + 200). </Td> </Tr> <Tr> <Td> Dodrabicentennial </Td> <Td> Alternative Latin form of Dodransbicentennial </Td> </Tr> <Tr> <Td> Dequasbicentennial </Td> <Td> Alternative Latin form of Dodransbicentennial </Td> </Tr> <Tr> <Td> Dosquicentennial </Td> <Td> Dosquicentennial has been used in modern times and this is perhaps a modern contraction of "de-quadrans". However, it seems inappropriate to combine the terms que and de when dealing with such Roman fractions . In any event, if such a conjunction was appropriate then it would perhaps more likely have been "Dosquibicentennial" (but the result is little shorter anyway). </Td> </Tr> <Tr> <Td> Demisemiseptcentennial </Td> <Td> Probably a modern coined term: demisemiseptcentennial; literally one - half (demi -) × one - half (semi -) × seven (sept -) × 100 years (centennial)--also demisemiseptcentenary . </Td> </Tr> <Tr> <Td> Quartoseptcentennial </Td> <Td> Probably a modern coined term: quartoseptcentennial; literally one - quarter (quarto -) × seven (sept -) × 100 years (centennial)--also quartoseptcentenary . </Td> </Tr> <Tr> <Td> Terquasquicentennial </Td> <Td> First used by Bell Laboratories in celebrating its 175th anniversary as a corporation . Is a coined word for an anniversary of 175 years, but the elements of the word literally refer to an anniversary of 375 years, as follows: ter - (3) × quasqui - (11⁄4) × centennial (100 years) </Td> </Tr> <Tr> <Td> Septaquintaquinque - centennial </Td> <Td> Suggested by lexicographer Robert L. Chapman to William Safire; first appeared in Safire's column, "On Language" (The New York Times Magazine, February 12, 1995). It is a coined word for an anniversary of 175 years, but the elements of the word literally refer to an anniversary of 35,000 years, as follows: septaquinta - (70) × quinque - (5) × centennial (100 years) </Td> </Tr> <Tr> <Td> 200 years </Td> <Td> Bicentennial </Td> <Td> Bicentenary </Td> <Td> </Td> </Tr> <Tr> <Td> 250 years </Td> <Td> Sestercentennial </Td> <Td> - </Td> <Td> To express 21⁄2 in Latin it would be expressed as "half - three". The term relates to being halfway (from the second) to the third integer . In Latin this is "Sestertius" which is a contraction of semis (halfway) tertius (third)--hence Sestercentennial . </Td> </Tr> <Tr> <Td> Semiquincentennial </Td> <Td> Probably a modern coined term: semi - (half) × quin (5) × centennial (100 years) = 250 years . Used by Brown University in 2015 . </Td> </Tr> <Tr> <Td> Bicenquinquagenary </Td> <Td> Used by Princeton University in 1996, Reading, Pennsylvania in 1998, and Washington and Lee University in 1999 . It is a coined word for an anniversary of 250 years: bi - (2) × cen (t) - (100) + quinquagenary (50 years). </Td> </Tr> <Tr> <Td> Quarter - millennial </Td> <Td> Meaning one quarter of one thousand years . </Td> </Tr> <Tr> <Td> 300 years </Td> <Td> Tercentenary / Tricentenary </Td> <Td> Tercentennial / Tricentennial </Td> <Td> </Td> </Tr> <Tr> <Td> 350 years </Td> <Td> Sesquarcentennial </Td> <Td> </Td> <Td> A modern coined term; sesquarcentennial for 350 years is deduced here from the "Sestertius" definition for 250 years above . For 350 years it relates to being halfway from the third to the fourth integer; thus a contraction of semis (halfway) and quartus (fourth); hence Sesquarcentennial . </Td> </Tr> <Tr> <Td> Semiseptcentennial </Td> <Td> Probably a modern coined term: semi - (half) × sept (7) × cen (t) - (100) × centennial (350 years) </Td> </Tr> <Tr> <Td> 400 years </Td> <Td> Quadricentennial </Td> <Td> Quadricentenary / Quatercentenary </Td> <Td> </Td> </Tr> <Tr> <Td> 500 years </Td> <Td> Quincentenary </Td> <Td> Quincentennial </Td> <Td> </Td> </Tr> <Tr> <Td> 600 years </Td> <Td> Sexcentenary </Td> <Td> Sexacentennial </Td> <Td> </Td> </Tr> <Tr> <Td> 700 years </Td> <Td> Septcentennial </Td> <Td> Septuacentennial </Td> <Td> Probably a coined term; earliest known use in March 1988 . Chiang Mai Septcentennial Stadium (Chiang Mai, Thailand) was completed in 1991 . </Td> </Tr> <Tr> <Td> 800 years </Td> <Td> Octocentenary </Td> <Td> Octocentennial </Td> <Td> </Td> </Tr> <Tr> <Td> 900 years </Td> <Td> Nonacentennial </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> 1000 years </Td> <Td> Millennial </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> 1500 years </Td> <Td> Sesquimillennial </Td> <Td> </Td> <Td> Term broken down as sesqui - (one and a half) millennial (1000 years) </Td> </Tr> <Tr> <Td> 2000 years </Td> <Td> Bimillennial </Td> <Td> </Td> <Td> </Td> </Tr> </Table> <Tr> <Th> Anniversary </Th> <Th> Latin - derived term </Th> <Th> Other terms </Th> <Th> Comments </Th> </Tr>

How many years is quarter of a century