1. Occurrences, circumstances, or facts that are perceptible by the senses.
2. Unusual, significant, or unaccountable facts or occurrences; marvels.

Something perceived or experienced; especially, an object as it is apprehended by the human senses.

". . . it was later realized that the phenomenon of changing air pressure had accounted for the variations in temperature readings in the open thermoscopes."

1. A natural event or occurrence that is recognized or known through the senses, not by intuition: Snow is a phenomenon of winter.
2. A remarkable, talented, and unusual individual or event: Beethoven was considered to be a phenomenon among musicians.

The normal plural form of phenomenon is supposed to be phenomena; however, phenomenons is also usually acceptable when referring to people or things: Reckless speculators are phenomenons among today's investors.

Phenomena is the correct plural form for scientific content: The phenomena were observed by astronomers throughout the world.

Tomorrow's weather forecast calls for several atmospheric phenomena.