User blog comment:B214/Question and Answers 6/@comment-26293136-20161029205102/@comment-74.56.202.110-20161109220203

Well tbh it doesn't seem like a sacred gear is considered a longinus based on it's potential/abilities to kill a god, but rather by how broken it is compared to other sacred gear. Sacred gears are comparable to geke genkai in naruto: while the average geke genkai goes from ice mirror to lava shower, the uchiha's lets you summon a 300ft tall flamming samurai capable of cutting down mountains. This is the same thing for sacred gears: while the average sg goes from creating swords to dragon king armor, Some of them give you the power of a heavenky dragon the power of god himself in the shape of a spear.

That's basiclly it. Longinus is just a term to descrbie those sacred gears that are deemed as op and broken.