WordNet
n. all non-artificial phenomena
Usage examples of "natural phenomenon".
He himself usually waited a long time before deciding on a name for a natural phenomenon or a connexion between phenomena which he had discovered.
Each probe was disguised, camouflaged, as a natural phenomenon so as not to alarm the local inhabitants.
Was I going towards a natural phenomenon as yet unknown to the savants of the earth?
It's a natural phenomenon that has existed for as long as the Earth has had an atmosphere.
For all we know, these harmless emissions may be the first overtures of an entirely new species of being, or evidence of a previously unknown natural phenomenon, and we would do ourselves and our mission a grave disservice if we prematurely cut ourselves off from that evidence out of fear and distrust.