1. being number forty in a sequence; 40th

1. the fortieth item in a series
2. one of forty equal parts of something

Examples

• She celebrated her fortieth birthday last month.
• The fortieth president of the United States was Ronald Reagan.
• He finished in fortieth place in the marathon.
• Today marks the fortieth anniversary of their wedding.
• The fortieth student to arrive got the last seat.
• Each heir received a fortieth of the estate.
• The fortieth chapter contains the book’s conclusion.