adverbial N2 common casualpolitewritten

一切〜ない — not at all / not in the least ~

一切〜ない・いっさいない

Meaning

not at all / not in the slightest / none whatsoever — a strong, categorical denial that rules out every instance

事故じこについて、会社かいしゃは一切いっさい説明せつめいしなかった。

The company gave no explanation at all about the accident.

Attaches to	Form	Example
一切 + (object) + negative predicate	一切 + 〜ない / 〜ません	一切いっさい知しらない / 一切いっさい認みとめない

私わたしはこの件けんに一切いっさい関係かんけいありません。

I have absolutely nothing to do with this matter.

店内てんないでの撮影さつえいは一切いっさい禁止きんしです。

Photography inside the store is strictly forbidden.

一切いっさい originally means 'everything / the whole', so with a negative it sweeps the entire range to zero. With an affirmative it instead means 'everything' (費用ひようは一切いっさい込こみ, 'all costs included').

Jengo shows 一切〜ない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.

Sources Compiled with reference to A Dictionary of Advanced Japanese Grammar.