信口开河

Pronunciation: xìn kǒu kāi hé Literal meaning: Let the mouth run free

Origin & Usage

信 here is giving free rein rather than trusting — the same use as in 信手拈来 — so the mouth (口) is doing whatever it likes. The second half is a pun that stuck: the Yuan original is 信口开合, letting the mouth simply open (开) and close, and 合 was later replaced by its homophone 河, which turned an image of jaws working into one of a river let loose. Both readings now sit in the phrase. The person who talks confidently and at length about things they have not looked into — and it works as a real accusation, not that they are lying but that they do not care whether it is true.

Examples

English: "He tends to make things up without any evidence."

Chinese: 他经常信口开河，没有任何依据。