a.

1. 緊要的，關鍵性的，危急的
   That was a critical time in the nation's history.

   那是涉及國家命運的一個關鍵時刻。

2. 批評的，批判的，評論性的
   Your critical analysis helped me a great deal.

   你的評論分析對我幫助很大。

3. 吹毛求疵的，愛挑剔的；對……表示不滿的[（+of）]
   She is so critical that nobody can get along with her.

   她很愛挑剔，沒有人能和她相處得來。

4. 必不可少的；緊缺而必須的
   His attendance is critical to the success of the meeting.

   他的出席對於這次會議的成功是必不可少的。

adj.

1. expressing adverse or disapproving comments or judgements.
2. expressing or involving an analysis of the merits and faults of a work of literature or art.
3. (of a situation or problem) at a point of crisis.
   ▸extremely ill and at risk of death.
   ▸having a decisive importance in the success or failure of something.
4. Mathematics  & Physics  relating to or denoting a point of transition from one state to another.
5. (of a nuclear reactor or fuel) maintaining a self-sustaining chain reaction.