ninth

I. ninth¹ /naɪnθ/ BrE AmE adjective
coming after eight other things in a series:
in the ninth century
her ninth birthday
—ninth pronoun:
I’m planning to leave on the ninth (=ninth day of the month).

Oxford Advanced Learner's Dictionary

ninth

ninth [ninth ninths] ordinal number, noun [naɪnθ] [naɪnθ]

ordinal number

9th There are examples of how to use ordinal numbers at the entry for fifth.

noun

each of nine equal parts of sth

Cambridge Advanced Learner's Dictionary

Cambridge Advanced Learner's Dictionary - 4th Edition

ninth / naɪnθ / ordinal number

A2 9th written as a word:

The ninth letter of the alphabet is I.

The school term ends on the ninth ( of July).

She was/came ninth in the national finals.

Collins COBUILD Advanced Learner’s English Dictionary

ninth

[na͟ɪnθ]
♦♦
ninths
1) ORD The ninth item in a series is the one that you count as number nine.
  ...January the ninth.
  ...students in the ninth grade.
  ...ninth century illustrated manuscripts.
2) FRACTION A ninth is one of nine equal parts of something.
  In Brussels the dollar rose by a ninth of a cent...
  What you see is only the tip. Eight ninths of it is under the sea.

Merriam-Webster's Advanced Learner's Dictionary

Merriam-Webster's Advanced Learner's Dictionary:

ninth

²ninth adj : occupying the number nine position in a series
• on the ninth day
• the book's ninth edition
• She's in (the) ninth grade at school.
- ninth adv
• He finished ninth in the race.
• the country's ninth largest city