ぜんぜん全然zenzen
1.

A term that communicates a complete or total denial, often used in conjunction with negative expressions to indicate that something is entirely absent or lacking.

2.

A word occasionally used in casual speech to emphasize a high degree or extent of something, expressing that it is exceptionally true or significant.

3.

An expression that conveys the feeling of being entirely untroubled or unconcerned about a situation, often dismissing any negative implications.

Example:

「長い1日だったのでお疲れでしょう」「いいえ、全然」