1570s, "a fact directly observed, a thing that appears or is perceived, an occurrence," especially a regular kind of fact observed on certain kinds of occasions, from Late Latin phænomenon, from Greek phainomenon "that which appears or is seen," noun use of neuter present participle of phainesthai "to appear," passive of phainein "bring to light, cause to appear, show" (from PIE root *bha- (1) "to shine").

Etymology [ edit] From Late Latin phaenomenon (“appearance”), from Ancient Greek φαινόμενον (phainómenon, “thing appearing to view”), neuter present middle participle of φαίνω (phaínō, “I show”).

Where does the noun phenomenon come from? Earliest known use late 1500s phenomenon is a borrowing from Latin. Etymons: Latin phaenomenon.

Etymology Late Latin phaenomenon, from Greek phainomenon, from neuter of phainomenos, present participle of phainesthai to appear, middle voice of phainein to show — more at fancy

The first records of the word phenomenon come from the 1580s. It comes from the Greek phainómenon, from the verb phaínesthai, meaning “to appear, become visible,” from phaínein, “to show, bring to light, make known.”