Probjectile

The probjectile was a weapon suggested by Tom Hall in the original design document for Doom, the Doom Bible. Its name is a of "probe" and "projectile" as the weapon was to fire a probe which was meant to be able to attach to monsters and some types of devices in order to either provide a statistics read-out on the creature, or in the case of machinery, potentially interfere with its functionality and destroy it. It was to occur in episodes three through six of Doom itself, as well as in the commercial sequel. Its description in the Doom Bible is as follows:

The probjectile was critical to the plot outlined for the commercial game in the Doom Bible, as it would have been required to finally destroy the General Demon and the ancients he had summoned, via firing its probe into a gap in the General's infernal machine during the game's conclusion. Despite this assigned importance, it was one of the earliest concepts from the Doom Bible to hit the cutting room floor. The only known resources for it exist in the Doom v0.2 IWAD in the and  lumps, which would have provided the icon and weapon name for the game's helmet visor HUD.

Trivia
In section 14 of the Doom Bible, the name of the weapon is misspelled as "probiectile." This is the only occurrence of that misspelling, but because it occurs in the main list of weapons, the weapon is sometimes called by this apparently incorrect name.