万まん々まん

also: ばんばん

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Meanings

Emphatic adverb meaning 'very much' or 'fully'. Often used with verbs like 違う, 結構, or 承知.

Used with a negative verb to mean 'never' or 'not at all'. Often in the pattern 万々～ない.

〈事こと〉〉は万々承知まんまんしょうちだto be fully aware of something
そんなことは万まん々まん承しょう知ちだ。
I'm fully aware of that already.
万々まんまん〈事こと〉はないはないthere is absolutely no chance of something happening
そんな失しっ敗ぱいは万まん々まんあり得えない。
Such a mistake could never happen.
万々違まんまんちがうto be completely different
二人ふたりの意い見けんは万まん々まん違ちがっていた。
The two opinions were completely different.

決けっしてN4sense 2
決して is the standard modern word for emphatic 'never' with a negative verb, while 万々 is a stronger, more literary variant used in the same pattern.
全まったくN3sense 1
全く is a common, neutral way to say 'completely' or 'entirely', while 万々 is a rarer, more emphatic and literary word used for the same intensifying sense.
全ぜん然ぜんN5sense 2
全然 is a casual, everyday way to say 'not at all', whereas 万々 conveys the same idea with heavier emphasis and a more formal, old-fashioned tone.

満まん々まん
満々 (まんまん) means brimming full of a feeling, while 万万 (まんまん), pronounced the same, is an adverb meaning 'utterly' or 'by no means' and almost always appears with a negative like 万万ない.

Reduplication of 万 (man, 'ten thousand'), emphasizing a large degree or absolute negation.