with a single blow; with one stroke
Describes defeating, destroying, or knocking down someone or something in one decisive hit. Often used in dramatic or emphatic contexts.
He knocked down his opponent with a single blow.
The swordsman cut down his enemy with one stroke.
Alternate spelling using 下に; less common but still encountered.
Phrase composed of 一撃 (ichigeki, 'one blow') + の (possessive particle) + もとに (moto ni, 'under/based on'), literally 'under one blow'. The exact historical derivation is uncertain, but it functions as an adverbial phrase meaning 'with a single blow'.