eighteenth

American  

[ey-teenth] / ˈeɪˈtinθ /

adjective

1. next after the seventeenth; being the ordinal number for 18.

2. being one of 18 equal parts.

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noun

1. an eighteenth part, especially of one (1/18).

2. the eighteenth member of a series.

eighteenth British  

/ ˈeɪˈtiːnθ /

adjective

1. (usually prenominal)

   1. coming after the seventeenth in numbering or counting order, position, time, etc; being the ordinal number of eighteen: often written 18th

   2. ( as noun )

      come on the eighteenth

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noun

1. 1. one of 18 approximately equal parts of something

   2. ( as modifier )

      an eighteenth part

2. the fraction that is equal to one divided by 18 ( 1/ 18 )

Etymology

Origin of eighteenth

before 900; Middle English eightenthe, eightethe, Old English eahtatēotha. See eighteen + -th ²

Example Sentences

The Dow Jones Industrial Average reached 48,500 points, marking its eighteenth record high of the year, reflecting market optimism.

From Barron's • Dec. 11, 2025

It’s the negative image of an important intellectual movement of the seventeenth and eighteenth centuries, the Enlightenment, whose principles formed, among other things, the basis for American democracy.

From Salon • Jun. 25, 2025

The Garrick was founded in 1831, named after famous eighteenth century actor David Garrick.

From BBC • Mar. 20, 2024

The scrolls were discovered in the eighteenth century, when workmen came across the remains of a luxury villa that might have belonged to the family of Julius Caesar’s father-in-law.

From Scientific American • Oct. 17, 2023

This makes accurate clocks indispensable on ocean voyages, but it wasn’t until the eighteenth century that accurate clocks became a reality.

From "Shipwreck at the Bottom of the World" by Jennifer Armstrong