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brandistock

n. A short polearm that has three retractable blades concealed in its handle, which are sprung upon a thrusting action forming a three-pronged spear.

Wikipedia
Brandistock

A brandistock (also called brandestoc, buttafuore or feather staff) was a short type of pole weapon which was used by both infantry and civilians alike, primarily police officers in Italy between the 16th and 19th centuries. Measuring some 5 feet long, the brandistock construction was unique for polearms in that it had a retractable blade. The head consisted of either a single or a trio of long thin points, which were kept in a hollow aperture inside the rest of the shaft. A sharp thrust of the weapon forward propelled the heads out, where they could be readily locked in place. This weapon is essentially a spear with a sliding blade, or alternatively, a long handled out-the-front gravity knife.