1. being number 90 in a sequence; coming after eighty-nine others

1. the person or thing that is number 90 in a sequence
2. one of 90 equal parts of something

Examples

• She celebrated her ninetieth birthday last week.
• The ninetieth day of the year falls in March or April.
• He finished in ninetieth place out of 200 runners.
• The ninetieth student to register received a prize.
• Only one ninetieth of the budget was allocated to that project.
• The ninetieth anniversary of the school will be celebrated next year.