If you describe something as unforgettable, you mean that it is, for example, extremely beautiful, enjoyable, or unusual, so that you remember it for a long time. You can also refer to extremely unpleasant things as unforgettable. A visit to the Museum is an unforgettable experience the leisure activities that will make your holiday unforgettable. + unforgettably un·for·get·tably an unforgettably unique performer. an unforgettable experience, sight, etc affects you so strongly that you will never forget it, especially because it is particularly good or beautiful