Eight/eɪt/ Definition 1 of 5Pro Tip 1/3Age Milestone Used to signify important childhood ages, such as starting school or becoming a teen. My son's turning eight; he's so excited! Pro Tip 2/3Math Operations Used in math to learn addition and multiplication. Remember its evenness. What's eight minus two? Pro Tip 3/3Counting Sequence Understanding its place in sequence helps in counting objects and telling time. Let's meet at eight past nine.