fourth

I. fourth¹ /fɔːθ $ fɔːrθ/ BrE AmE adjective
[Language: Old English; Origin: feortha, from feower 'four']
coming after three other things in a series:
in the fourth century
her fourth birthday
—fourthly adverb
II. fourth² BrE AmE pronoun
the fourth thing in a series:
the fourth of July

Oxford Advanced Learner's Dictionary

fourth

fourth [fourth fourths] ordinal number, noun [fɔːθ] [fɔːrθ]

ordinal number

4th There are examples of how to use ordinal numbers at the entry for fifth.

noun (especially NAmE) = quarter
Example Bank:
• a fourth of the city population

• one fourth of total sales

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

fourth / fɔːθ / / fɔːrθ / ordinal number

A2 4th written as a word:

My birthday is on the fourth ( of December).

Daniel was/came fourth in the race.

Collins COBUILD Advanced Learner’s English Dictionary

fourth

[fɔ͟ː(r)θ]
♦♦
fourths
1) ORD The fourth item in a series is the one that you count as number four.
Last year's winner Greg Lemond of the United States is in fourth place.
2) FRACTION A fourth is one of four equal parts of something. [AM]
Three-fourths of the public say they favor a national referendum on the issue.(in BRIT, use quarter)

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

fourth

²fourth adj
1 : occupying the number four position in a series
• on the fourth day
• the book's fourth edition
• her fourth goal of the season
2
- used to refer to one of the forward gears or speeds of a vehicle
• fourth gear
- fourth adv
• She finished fourth in the race.
• the fourth highest mountain