FLEETING
- ephemeral (correct answer)
- hurried
- slight
- temporary
Explanation: FLEETING has a somewhat poetic or philosophical connotation, meaning lasting for a very short time. 'Ephemeral' shares this specific connotation and is often used in a similar context. 'Temporary' is a more common, neutral word that lacks the sense of something passing away quickly. 'Hurried' implies haste, not just short duration. 'Slight' refers to degree, not time.