Word: 一心 (yīxīn)

一心不可二用。

Yìxīn bùkě èr yòng.

You can't do two things at once.

她一心扑在工作上。

Tā yìxīn pū zài gōngzuò shàng.

She has thrown herself heart and soul into her work.

家有一心，堆积黄金；家有二心，无钱买针

jiā yǒu yìxīn, duījī huángjīn; jiā yǒu èrxīn, wú qián mǎi zhēn

a family of one heart piles up gold; a family of two hearts can't afford a needle