Onetime (often written as “one-time”) describes something that happens only once, not repeatedly. A one-time fee is a single payment, not a monthly charge. A one-time event won't happen again.

When a school holds a one-time assembly to celebrate winning the state championship, they're marking a special occasion that won't repeat. When a store offers a one-time discount, customers can only use it once. A scientist might observe a one-time phenomenon in an experiment, something that appeared once but never again, making it difficult to study or verify.

The word can also describe someone's former role or identity. A one-time champion is someone who once held that title but no longer does. A one-time friend might be someone you were close to in the past but aren't anymore.

Be careful not to confuse onetime with “on time,” which means punctual or not late. They sound similar but mean completely different things: arriving on time for a one-time performance means you showed up punctually for an event that will only happen once.