勢い・勢|いきおいikioi[3]nakadaka (mid-high)

1. nounforce; vigor; vigour; energy; spirit; life
   あらしの勢いきおいが弱よわまった。↗

   The storm abated.
2. nouninfluence; authority; power; might
3. nounimpetus; impulse; momentum; course (of events)
   勢いきおいに流ながされているんですよ。↗

   You are carried along with the slide.
4. adverbnaturally; necessarily; inevitably

• Synonym力ちからNeutralThe broadest of these words, covering physical strength and ability in general; 「勢い」 instead stresses the impetus of something moving or gaining ground.
• Synonym推進力すいしんりょくNeutralThe force that pushes things forward, as in 「改革の推進力」; it highlights what drives progress and leans toward written or formal use.
• Related強さつよさNeutralThe degree or intensity of being strong, as in 「風の強さ」; it measures how strong something is, while 「勢い」 is the dynamic drive or momentum of something in motion.
• Antonym衰えおとろえNeutralDecline or weakening, as in 「体力の衰え」; it stands as the direct opposite of 「勢い」.
• Antonym弱りNeutralThe state of having grown weak; it contrasts with the vigor of 「勢い」 but is rarely used on its own in everyday speech.

Use 「勢い」 for the drive or momentum of something in motion. For sheer degree of strength pick 「強さ」, for strength or ability in general 「力」, and for the force pushing something forward 「推進力」. The opposite of 「勢い」 is 「衰え」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 物事ものごとを行おこなう際さいの強つよい力ちからや活発かっぱつさ。
2. 他者たしゃや社会しゃかいに対たいして持もつ影響力えいきょうりょくや支配しはい力りょく。
3. 動うごいているもの或いはあるいわ進行中しんこうちゅうの事柄ことがらが持もつ推し進おしすすめる力ちから。
4. そうなるしかない状態じょうたい。当然とうぜんのこと。