The graceful self-host and blue stocking, Yaxin, explains the origin of the subject term.

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PS: The term "blue stocking" refers to women who are learned and intelligent, though sometimes they are not appreciated by men. (Yaxin is an exception.)

Some other English terms may let you think of them just as their names imply, but they are not. For example:

red tape: bureaucratically official rules

Toilet water: a kind of perfume

Sweet water: limpid water

loose cannon: a potentially powerful man

rough diamond: a person who has many good qualities but has not appeared.

personal remark: an abusive remark against others personally

confidence man: an imposter.

Etc.....