Learner's definition of RAZOR
a tool or device with a sharp edge that is used to shave or cut hair from the face, body, or head
see picture at grooming
— used in various phrases to refer to a dangerous position or a position in which two different things are carefully balanced
He's a thrill-seeker who likes living on the razor's edge.
The country's future is balanced on a razor's edge.
He walks a/the razor edge [=walks a/the fine line] between humor and bad taste in his comedy.