also: いちびんいっしょう
noun
mood; caprice; a smile or a frown
A yojijukugo meaning one's mood or whims, literally 'one frown, one smile'. It refers to the subtle changes in a person's expression that reveal their feelings or capricious nature. Often used in literary or formal contexts.
彼女の一顰一笑に、周囲はいつも振り回されている。
Everyone around her is always swayed by her every mood and whim.
上司の一顰一笑を気にするあまり、自由に意見が言えない。
I'm so concerned about my boss's every frown and smile that I can't speak freely.