EPHEMERAL

Concept

An antonym is a word whose core meaning is opposite to that of another word.

For a duration word, compare whether each choice expresses brevity, permanence, or an unrelated quality.

Application

Ephemeral means lasting for a very short time. Eternal means continuing forever or without end, so the two words lie at opposite ends of the duration scale.

Contrast

• Transient means temporary or passing quickly, which is close in meaning to ephemeral.

• Short-lived means lasting only briefly, which is also close in meaning to ephemeral.

• Eternal means lasting without end, which reverses the brief-duration sense of ephemeral.

• Trivial means unimportant; it describes significance, not duration.

Cross-check

Replacing ephemeral with eternal changes the duration from brief to unending, whereas transient and short-lived preserve the original idea and trivial changes the meaning axis.

Therefore, the most opposite word is Eternal.