What does fifteenth mean?
Fifteenth is the ordinal form of the number fifteen, indicating the item or person that occupies position fifteen in any ordered sequence. It functions chiefly as an adjective, as in 'the fifteenth chapter' or 'the fifteenth of March', but it can also serve as a noun denoting the member of a series in that position, or a fraction formed by dividing something into fifteen equal parts. In everyday use it appears most often with dates, anniversaries, floors of buildings, and numbered editions or amendments — most famously the Fifteenth Amendment to the United States Constitution, ratified in 1870, which prohibited denying citizens the vote on grounds of race. Historically, 'the fifteenth century' is a fixed phrase referring to the years 1401 to 1500, a period often associated with the early Renaissance. Musicians use the term differently: a fifteenth is an interval spanning two octaves. The word is neutral in tone, equally at home in formal writing and casual speech, and follows the standard pattern by which English builds ordinals from cardinal numbers ending in '-teen'.
Coming after the fourteenth in order; corresponding to the number fifteen in a series (15th).
"Their office is on the fifteenth floor."
Often written as the numeral plus suffix '15th' in dates, lists, and informal contexts.
A person or thing in the fifteenth position, or one of fifteen equal parts of a whole.
"Only a fifteenth of the budget remained unspent."
In music, a 'fifteenth' isn't an interval at all — it's two octaves up, because stacking two octaves lands you on the fifteenth scale degree.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fifteenth
Fifteenth derives from the Old English ordinal 'fiftēoþa', formed from 'fiftene' (fifteen), which combines 'fīf' (five) with the '-tēne' suffix meaning 'ten more than'. The root traces back to the Proto-Germanic '*fimf', from the Proto-Indo-European '*penkwe', the same ancient root that produced Greek 'pente' (as in pentagon) and Latin 'quinque' (as in quintet). English replaced the native Germanic ordinal ending with the '-eth' suffix during the Middle English period, yielding the modern form.
How fifteenth is actually used
As an ordinal adjective it is written either 'fifteenth' or '15th'; ordinals in formal prose are often spelled out for values below one hundred. The fractional sense ('a fifteenth') is rare compared to common fractions like 'half' or 'quarter' and appears mostly in technical or mathematical contexts.
Easily confused with fifteenth
'Fifteenth' refers to the ordinal number 15th, while 'fiftieth' refers to the ordinal 50th.