saltpeter, niter, the mineral form of potassium nitrate (KNO₃).

gunpowder

one thing

(inorganic chemistry) ammonium nitrate

Shimose powder, a kind of picric acid-based explosive

kayakujutsu

first, initial / one-eyed

one-eyed goblin, a Japanese monster

“a hundred days of sermonizing, one fart” → a metaphor for how something that one has put great effort into can come to nothing after even a slight mistake, much as a hundred days of serious spiritual study can be lost to the winds