Half of needle hidden in backpack to provide retribution (7)

I believe the answer is:

kneecap

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'retribution' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'half of needle hidden in backpack' is the wordplay.
'half of' means to take half the letters.
'hidden in' is an insertion indicator.
'backpack' becomes 'kcap' ('pack' backwards).
'needle' halved is 'nee'.
'nee' placed inside 'kcap' is 'KNEECAP'.

'to provide' acts as a link.

Can you help me to learn more?

(Other definitions for kneecap that I've seen before include "Horribly punish" , "one going on bender?" , "The informal patella (7)" , "part of joint" , "Bone" .)

I've seen this clue in The Independent.

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