The story
From war + head, originally to distinguish a live war head of a torpedo from an inert exercise head. Piecewise doublet of war chief.
Etymology from Wiktionary, CC BY-SA 4.0.
warhead
Today it means: The part of a missile, projectile, torpedo, rocket, or other munition which contains either the nuclear or thermonuclear system, high explosive system, chemical or biological agents, or inert materials intended to inflict damage. Full definition →