eighteenth

American  

[ey-teenth] / ˈeɪˈtinθ /

adjective

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

2. being one of 18 equal parts.

---

noun

eighteenths plural

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

---

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 )

Other Word Forms

Noun Inflected Forms

• eighteenths
  plural

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

In the early eighteenth century, Georgia and Virginia used fines to penalize people for not voting.

From Salon • Dec. 31, 2024

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

Chemistry, too, became more scientific and less mystical as the eighteenth century wore on.

From "The Scientists" by John Gribbin