일은 아니지만

it's not a …, but

→ 일
phrase Uncommon #9,153
it's not a …, but 일 means “thing,” “matter,” or “task”; the word before 일 describes what kind of thing or task it is.
KO: 쉬운 일은 아니지만 해볼게요.
EN: It's not an easy task, but I'll give it a try.