The antonyms of *achievable* are *impossible* and *unattainable*. *Impossible* means that something cannot be done under any circumstances, while *unattainable* suggests that something may be possible but is beyond one's reach or ability. Use these words to set realistic goals, describe the feasibility of solutions to problems, and motivate oneself or others to pursue attainable goals or push beyond limits.

시간을 거슬러 올라가는 것은 *불가능*합니다.

時間を遡ることは*不可能です*。

It's *impossible* to travel back in time.

어떤 사람들에게는 백만장자가 되는 것이 *이룰 수 없는* 꿈입니다.

一部の人々にとって、億万長者になることは*達成不可能な*夢です。

For some people, becoming a millionaire is an *unattainable* dream.