口若悬河

kǒu ruò xuán hé

to talk a blue streak; very eloquent

Character by character

口kǒu
mouth

若ruò
like

悬xuán
hanging

河hé
river

他一讲起历史就口若悬河，停都停不下来。

Once he starts on history, the words pour out and he can't stop.

Tone: neutral.

A waterfall of words: praise for eloquence, or a dig at a smooth talker.

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