eighteenth

eight·eenth [eighteenth eighteenths] [ˌeɪˈtiːnθ] ; [ˌeɪˈtiːnθ] ordinal number, noun There are examples of how to use ordinal numbers at the entry for fifth.

Main entry: eighteenderived

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

eighteenth / ˌeɪˈtiːnθ / ordinal number

18th written as a word:

Next Monday is the eighteenth ( of February).

Collins COBUILD Advanced Learner’s English Dictionary

eighteenth

[e͟ɪti͟ːnθ]
♦♦
ORD
The eighteenth item in a series is the one that you count as number eighteen.
The siege is now in its eighteenth day.

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

eighteen

eigh·teen /ˌeɪtˈtiːn/ noun, pl -teens [count] : the number 18
- eighteen adj
• eighteen years
- eighteen pronoun
• Eighteen (of them) were present.
- eigh·teenth /ˌeɪtˈtiːnɵ/ noun, pl -teenths [count]
• one eighteenth of the total
- eighteenth adj
• the eighteenth day
- eighteenth adv
• He finished eighteenth in the race.