If something is extraordinary, remarkable, or one of a kind, you can say it is singular. A singular opportunity to sing onstage with a rock star is a remarkable opportunity.
Seeing the single inside singular can help you understand its meaning in the sense of one. In grammar, singular means one, as opposed to plural, which means more than one. But singular’s not always––or singularly––about being unique. Walking through a foggy cemetery might give you a singular feeling––or a feeling that’s odd and peculiar––that ghosts could possibly be real.