1. being number thirty in a sequence; 30th

1. the ordinal number matching the number thirty in a sequence
2. one of thirty equal parts of something

Examples

• Today is my thirtieth birthday.
• She finished in thirtieth place in the marathon.
• The thirtieth chapter of the book was the most exciting.
• He was the thirtieth person to sign up for the class.
• Only one thirtieth of the population voted in the election.
• The meeting is scheduled for the thirtieth of June.