Doublade resembles two swords sheathed on a plaque. Each sword has a pink eye with a black, linear pupil on the hilt, as well as a pink, tassel-like arm emerging from the handle. The swords are able to communicate telepathically, and they use this ability to carry out complex attacks that are unstoppable even to those skilled at swordplay.
Doublade appears to be based conceptually on a pair of fully sentient, possessed magical swords. Considering the crossed swords and shield connecting the Pokémon together, it is probably based on a coat of arms. The fact that it started off as an ordinary sword as a Honedge may mean it could be based on the bushido mythos behind katana use; katanas possessed the user samurai's soul and attacked of its own free will. Visually, considering its build and hilt, Doublade seems to be based on a pair of either spatha, claymore, or possibly jian swords with their own scabbards, tassel-like prehensile limbs, and a shared shield connecting its scabbards together.
Doublade is a combination of double and blade.
Nidangill may be a combination of 二 ni (two), 断 dan (to sever), and 斬る kiru (to slay with a blade) or kill.