What is the plural of 'phenomenon'?

The plural of “phenomenon” is “phenomena.”

“Phenomenon” comes from Ancient Greek phainomenon, meaning something appearing or observed. Its traditional plural, “phenomena,” preserves the Greek neuter plural ending -a. In formal standard English, “phenomena” is the established plural when referring to multiple observed events, facts, or experiences.

For example, “The researchers recorded several unusual phenomena” treats each unusual event as a separate phenomenon. The singular and plural are pronounced differently: phenomenon is commonly /fə-NOM-ə-non/, while phenomena is commonly /fə-NOM-ə-nə/.

English also contains many borrowed plurals, and usage changes over time. Some speakers use “phenomena” as a singular, especially in scientific or academic writing, but traditional standard grammar treats it as plural. The regularized form “phenomenons” sometimes appears, particularly when writers are unfamiliar with the Greek pattern, but it is not the canonical plural in a general English quiz. “Phenomenae” and “phenomeni” are not standard plurals of this noun.