I stumbled upon 金口难开, and I think it's a 成语. I think it describes people who are pretentious (金口 = gold mouth), which makes it hard for them to speak (难开 = difficult to open).
Question: Is 金口难开 an idiom, and if so what would be a suitable CC-CEDICT definition?
Here's my partial CC-CEDICT definition (which I'm not very confident about):
金口难开 金口難開 [jin1 kou3 nan2 kai1] /lit. a gold mouth is hard to open (idiom)/fig. to be too pretentious for words/
which is modified from a related definition:
羞口難開 羞口难开 [xiu1 kou3 nan2 kai1] /to be too embarrassed for words (idiom)/
PS: CC-CEDICT definitions need to be high-quality (they're used in dictionaries all over the world). The whole dictionary is free to download. Submissions are reviewed prior to modifying the database. They have a specific syntax, e.g.:
中國 中国 [Zhong1 guo2] /China/Middle Kingdom/