Wear down to earth, as Her Majesty might say (5)

I believe the answer is:

grind

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'wear down' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for grind that I've seen before include "work for teeth?" , "Crush, oppress; hard work" , "Harshly rub together" , "Pulverise" , "Chore" .)

I've seen this clue in The Guardian.

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