이

Turns a verb into a thing's name

-이 makes a noun out of a verb, naming the tool or the person that does it: 연필깎이 'pencil sharpener' from 깎다 'to sharpen', 턱받이 'bib' from 받다 'to catch', 응석받이 'a spoiled child'. Fans use it to name an obsession too — 진진앓이 is 앓다 'to ache over' turned into a noun, roughly 'pining over Jinjin'. These are settled words you learn one at a time, not a pattern to apply freely.