also: けして
never; not at all; by no means
Always used with a negative predicate to form a strong denial or prohibition. Equivalent to 'never' or 'not in the slightest'.
He never tells a lie.
この問題は決して簡単ではない。
This problem is by no means easy.
He never tells lies.
You must never give this medicine to children.
Please never give up until the very end.
決して pairs with negatives to flatly state something will never happen, while どうしても in the same negative pattern stresses that it's impossible despite every effort.
決して~ない expresses a strong, determined negation ('never, absolutely not'), while 一度も~ない specifically stresses that an occurrence count is zero.
決して is the standard word for strong negation and pairs with negatives just like 誓って, but without the swearing nuance.
Kana spelling is common in informal writing and when the kanji is not needed.
Irregular kana usage; a colloquial or dialectal variant of けっして. Not standard.