Instrument knocking front off another (4)

I believe the answer is:

lute

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'instrument' is the definition.
(lute is a kind of instrument)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for lute that I've seen before include "Plucked, pear-shaped instrument" , "Old plucked instrument" , "Subject to drugs" , "Play instrument" , "Old stringed instrument with a pear-shaped body" .)

I've seen this clue in The Daily Express.

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