心事 (xīn shì) — a burden on one's mind, a worry (often kept to oneself)

Definition

Examples

• 他最近总是一个人发呆，好像有很多心事。
  Tā zuì jìn zǒng shì yí gè rén fā dāi, hǎo xiàng yǒu hěn duō xīn shì.
  He's been spacing out alone lately, as if he has a lot on his mind.
• 你有什么心事可以跟我说说，别憋在心里。
  Nǐ yǒu shén me xīn shì kě yǐ gēn wǒ shuō shuō, bié biē zài xīn lǐ.
  If you have something on your mind, you can tell me—don't bottle it up.
• 这件事一直是我的一桩心事，现在终于解决了。
  Zhè jiàn shì yì zhí shì wǒ de yì zhuāng xīn shì, xiàn zài zhōng yú jiě jué le.
  This matter has been a burden on my mind, and now it's finally resolved.

Origin