Milligan possibly loses his head to infantry weapon (4)

I believe the answer is:

pike

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'weapon' is the definition.
(I know that pike is a type of weapon)

I don't understand the remainder of the clue.

(Other definitions for pike that I've seen before include "Fish - long spear-like weapon" , "Long European freshwater predator" , "Imitating earlier style" , "Old spear or voracious lake fish" , "may be hooked" .)

I've seen this clue in The Independent.

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