Critical
Part of speech: adjective
Definition: Inclined to find fault or criticize; fastidious; captious; censorious; exacting. Pertaining to, or indicating, a crisis or turning point. Extremely important. Relating to criticism or careful analysis, such as literary or film criticism. Of a condition involving unstable vital signs and an unfavorable prognosis. Likely to go out of control if disturbed, that is, opposite of stable. Of the point (in temperature, reagent concentration etc.) where a nuclear or chemical reaction becomes self-sustaining.
Example sentence: Happiness is a critical factor for work, and work is a critical factor for happiness. In one of those life-isn't-fair results, it turns out that the happy outperform the less happy. Happy people work more hours each week - and they work more in their free time, too.
Scathing
Part of speech: verb
Definition: To injure or harm.
Part of speech: adjective
Definition: harshly or bitterly criticalharmful or painful; acerbic