Once in a lifetime Definition 1 of 2Pro Tip 1/3Non-recurring Event Use for events that don't repeat or are extremely rare, emphasizing their uniqueness. Witnessing Haley's Comet is a once in a lifetime event. Pro Tip 2/3Emotional Impact Describes moments that evoke strong feelings because of their rarity. Meeting my favorite author was a once in a lifetime experience. Pro Tip 3/3No Hyperbole Avoid overusing for common events; it loses impact if not truly rare. Landing a huge promotion felt like a once in a lifetime opportunity.