What does thirtieth mean?
“Thirtieth” is the ordinal number for thirty, used to identify the 30th item in a sequence. It appears naturally in expressions involving dates, birthdays, anniversaries, and other milestones, as in “the thirtieth of May” or “a thirtieth birthday.” It can also function as a noun meaning one of thirty equal parts, especially in mathematical or formal contexts: “She contributed a thirtieth of the amount.” The word is distinct from the cardinal “thirty,” which identifies the number itself rather than a position within a series. “Thirtieth” is useful because it combines the precise meaning of an ordinal with the familiarity and memorability of the number thirty.
Denoting the 30th member of a series.
"The thirtieth of May is the deadline for applications."
Used with dates, ages, anniversaries, and ordered sequences in standard British and American English.
One of thirty equal parts.
"She contributed a thirtieth of the total cost."
This is primarily a mathematical or formal use; the plural “thirtieths” is possible but less common.
Used when referring to multiple thirtieth parts; the ordinary ordinal and date uses generally do not require a plural.
"The estate was divided into thirtieths."
Adding “-th” turns the round number thirty into a precise milestone: the thirtieth.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does thirtieth come from?
“Thirtieth” is an English ordinal formed from “thirty” with the ordinal suffix “-th,” whose modern spelling reflects the historical development of Middle English ordinal forms. “Thirty” descends from Old English þritig, a Germanic numeral related to “three” and “thrice.” The shared numerical history is reflected in the modern distinction between the cardinal “thirty” and its ordinal derivative “thirtieth.”
How thirtieth is actually used
Standard in both British and American English. Its use for a fraction is mainly mathematical or formal, while its ordinal use is common in dates, anniversaries, ages, and sequences.
Easily confused with thirtieth
“Thirty” is the cardinal number, while “thirtieth” is the ordinal form meaning 30th in a sequence.