下 + 沉
The adjective 沉 (chén) can mean "heavy," "deep," or "sinking," depending on context. It describes physical weight, a sinking motion, or a somber mood. In geographical or structural contexts, it may describe land or buildings gradually subsiding.
这个箱子太沉了,我搬不动。
zhège xiāngzi tài chén le, wǒ bān bù dòng.
This box is too heavy; I can't move it.
天色沉下来,看样子要下雨了。
tiānsè chén xiàlái, kàn yàngzi yào xià yǔ le.
The sky darkened; it looks like it's going to rain.
他的心情很沉,一句话也不想说。
tā de xīnqíng hěn chén, yī jù huà yě bù xiǎng shuō.
His mood was heavy, and he didn't want to say a word.