Unit of frequency does some damage we hear (5)

I believe the answer is:

hertz

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'unit of frequency' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for hertz that I've seen before include "Cycles per second unit" , "A measure of frequency" , "Unit of frequency - German physicist, d. 1894" .)

I've seen this clue in The Globe and Mail.

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