Is 金口难开 an idiom, and if so what would be a suitable CC-CEDICT definition?

Question

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).

Examples:

1. 家长怎么教宝宝都是金口难开，多半是少做了这些事^[src]
2. 微信聊天，金口难开的女人无非有三个心理,摸准后她对你念念不忘 ^[src]
3. 金口难开，绝不会认错的星座! ^[src]

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)/

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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/

Answer 1

金口難開

..... 後來，便有了「金口難開」這個成語，表示：嘴巴像金子一樣珍貴，不輕易張口用來說話；形容一個人沉默寡言、不愛說話。

Base on the story, 金口難開 originally describe "someone value his own words like gold, do not open his mouth to speak unless it is necessary" ; Now it is used to describe "someone being reticent; a man of few words"

• 金口 = golden mouth (valuable speech)

• 難開 = 難得打開 (rarely open)

Answer 2

Is it an idiom?

Maybe?

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Is 金口难开 a chengyu? No I don't believe that it is. On one side of the coin 金口难开 could be considered a construct; in this case a phrase made-up of two different words: 金口 & 难开. In fact, 金口难开 doesn't really have an entry in any readily available dictionaries. Interestingly enough, though, the expression does show up as an example sentence in Pleco C-E under the entry of 金口:

金口难开
unable or unwilling to utter a word

Pleco C-E is a regularly updated and maintained dictionary that could easily add this headword if they deemed it to be an actual word in and of itself.

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Could a case be made that it is, in fact, a set phrase? Probably?

If this were deemed an idiomatic expression you might have an argument that it belonged in a dictionary.

FT Chinese has written an article with the headline:

“金口难开”的特朗普支持者

Is it in quotes to be ironic or is it because it is a set phrase that means something?

Sohu, similarly, also has an article with a similar headline:

两岁孩子仍然“金口难开”，父母该如何引导？

There is a section of the book《金牌营销必备丛书》with the heading:

面对“金口难开”型顾客的直销法

Overall, it seems like are more sarcastic undertones to this phrasage than is readily implied in its literal meaning. And, if you could prove that, then you'd have a much better case on your hand to argue for its right to have an entry as a headword.