Verifying which six must leave tip? (5)

I believe the answer is:

prong

'tip?' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for prong that I've seen before include "Tooth" , "Fork's point" , "Something piercing" , "Spur; projecting part" , "branch" .)

I've seen this clue in The Sun, The Telegraph and The Times.

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