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Phrase(s): *sharp as a razor
1. very sharp. (*Also: as ~.) • The penknife is sharp as a razor. • The carving knife will have to be as sharp as a razor to cut through this gristle. 2. and *sharp as a tack very sharp-witted or intelligent. (*Also: as ~.) • The old man’s senile, but his wife is as sharp as a razor. • Sue can figure things out from even the slightest hint. She’s as sharp as a tack.
McGrawhill's American Idioms And Phrasal Verbs