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fortieth

American  
[fawr-tee-ith] / ˈfɔr ti ɪθ /

adjective

  1. next after the thirty-ninth; being the ordinal number for 40.

  2. being one of 40 equal parts.

noun

  1. a fortieth part, especially of one (1/40).

  2. the fortieth member of a series.

fortieth British  
/ ˈfɔːtɪɪθ /

adjective

    1. being the ordinal number of forty in numbering or counting order, position, time, etc. Often written: 40th

    2. ( as noun )

      he was the fortieth
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

noun

    1. one of 40 approximately equal parts of something

    2. ( as modifier )

      a fortieth part

  2. the fraction equal to one divided by 40 ( 1/ 40 )

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of fortieth

before 1100; Middle English fourtithe, Old English fēowertigotha. See forty, -eth 2

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

It orbits extremely close to its star, at a distance just one fortieth that of Mercury from the Sun.

From Science Daily • Mar. 22, 2026

I recently booked a birthday trip to Europe for my fortieth birthday in 2023 and can’t cancel the plans or will lose out on the money.

From Slate • Sep. 12, 2022

"Administrators cite the omicron variant, but one report says omicron case fatality rate is one fortieth of that of the delta variant," Hurley added in the video.

From Fox News • Jan. 22, 2022

Find the fortieth term of a sequence where the first term is −19 and the common difference is seven.

From Textbooks • May 6, 2020

With only seconds to spare, Bobby just barely made his fortieth move against Bronstein before his flag fell, which otherwise would have caused him to be forfeited.

From "Endgame" by Frank Brady

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.