口干 (kǒu gàn) means “thirsty” | MotiTan Chinese Dictionary

More examples

天气干燥，我一会儿就口干。tiān qì gān zào wǒ yí huìr jiù kǒu gàn

In dry weather, I soon feel thirsty.

The mouth feels dry as the body registers a need for more fluid.

口渴kóu kě: Feeling thirsty and wanting to drink.
干燥gān zào: Lacking moisture and feeling dry, often describing air, skin, or other things.

口腔感到干燥，常伴随想喝水或唾液减少的感觉。kǒu qiāng gǎn dào gān zào cháng bàn suí xiǎng hē shuǐ huò tuò yè jián shǎo de gǎn jué

The two parts of 口干 (kǒugàn, "dry mouth") are 口 (kǒu, "mouth") and 干 (gān, "dry"), combining a body part with its lack of moisture.

English often expresses this kind of physical condition with a form of "be," but Chinese commonly lets the adjective serve directly as the predicate.