momentary

Compared meaning: lasting only a short time (adjective).

比较义项：持续时间很短（形容词）。

• brief

  Describes a short duration that is often planned or deliberate, especially events, speech, or visits; neutral to formal register; not typically used for sudden involuntary feelings.

  指持续时间短，常是经过安排或有意为之的，尤其用于事件、讲话或拜访；语域中性偏正式；通常不用于形容突然、不由自主的情绪。

  Please keep your speech brief so the ceremony doesn't run late.

  请把你的讲话保持简短，这样典礼就不会拖延。

• fleeting

  Emphasizes that something passes quickly and cannot be held onto, often used for abstract or intangible things like fame, youth, or a glimpse; slightly literary, tinged with wistfulness.

  强调事物转瞬即逝、无法留住，常用于名誉、青春或匆匆一瞥等抽象或无形的事物；语气略带文学性，常含惋惜意味。

  Beauty is fleeting, so she tried to enjoy every stage of her life.

  美丽是转瞬即逝的，所以她努力享受人生的每个阶段。

• momentary 本词

  Emphasizes an extremely short duration, often just a single instant; typically describes involuntary states or feelings such as panic, hesitation, or a lapse, not planned events.

  强调持续时间极短，往往只是一瞬间；通常用来形容不由自主的状态或情绪，如恐慌、犹豫或走神，而非有计划的事件。

  A momentary lapse in concentration caused him to miss his exit.

  一时的注意力不集中让他错过了出口。

Brief, fleeting, and momentary all describe a short time, but differ. Brief means a short, planned time, like a meeting or visit. Fleeting stresses something that passes quickly, for abstract things like fame or youth. Momentary means an extremely short time, like panic or hesitation.

这三个词都表示“持续时间短”，但语气和用法不同：brief强调可控、经安排的短暂，常用于会议、讲话或拜访；fleeting强调转瞬即逝、难以留住，常用于名誉、青春等抽象或美好事物，带文学色彩；momentary强调仅一瞬间，常形容不由自主的情绪或状态。这里不比较brief作名词（诉状）或动词（简要指示某人）的用法。