1. the numbers from 40 to 49, especially when referring to temperature, age, or years in a century
Usage: plural form
2. the period of someone’s life from age 40 to 49
Usage: plural form
3. the years from 1940 to 1949 in a century
Usage: plural form

Examples

• The temperature will be in the forties today.
• She’s in her early forties and very successful.
• My grandfather was born in the forties.
• The stock market crashed in the late forties.
• It’s supposed to stay in the low forties all week.
• He didn’t get married until his forties.
• Fashion in the forties was quite different from today.