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 \sharp as a razor.) •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.
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