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general::
Phrase(s): Better keep still about it. [and] Someone had better keep still about it.; Better keep quiet about it.; Someone better keep quiet about it.
A particular person ought not to tell about or discuss something. (The someone can stand for any person’s name, any pronoun, or even the word someone meaning "you-know-who." If there is no Someone had, the phrase is a mild admonition to keep quiet about something.) • Mary: I saw you with Bill last night. Jane: You’d better keep quiet about it. • Jane: Tom found out what you’re giving Sally for her birthday. Bill: He had better keep quiet about it!
McGrawhill's American Idioms And Phrasal Verbs