冴(さ)えない

dull; unimpressive; not going well

冴(さ)え渡(わた)る

to be crystal clear; to be exceptionally sharp

冴(さ)え返(かえ)る

to become clear and cold again

冴(さ)え切(き)る

to be completely lucid; to be exceptionally sharp

冴(さ)え冴(ざ)え

clearly; vividly; serenely

冴(さ)え上(あ)がる

to become clear; to clear up

彼(かれ)は危機的(ききてき)な状況(じょうきょう)でも、冴(さ)えた判断(はんだん)で事態(じたい)を収拾(しゅうしゅう)した。

Even in a critical situation, he brought things under control with his sharp judgment.

徹夜明(てつやあ)けなのに、頭(あたま)が冴(さ)える。

Even though I pulled an all-nighter, my mind is clear.