to eat / (archaic, humble) to eat or drink

one thing

all you can eat

food scraps, leftovers, leftover food

first, initial / one-eyed

one-eyed goblin, a Japanese monster

you should not interfere in a marital dispute

“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