The pronunciation is consistent in both American and British English, with the stress on the second syllable, which carries the "fem" sound.
The term "ephemeral" comes from the Greek word "ephemeros," which means "lasting only one day" or "short-lived." This word itself is derived from "epi-" meaning "on" and "hemera" meaning "day." The usage of "ephemeral" in English dates back to the late 16th century, capturing the transient, day-long nature of some life forms and phenomena, emphasizing the brief but significant impact they may have despite their short duration. This concept has expanded in modern usage to encompass a broader range of temporary phenomena, emphasizing the transient beauty and impermanence of such experiences.