미련이 · 미련을
lingering attachment, regret, not being able to let go
Example
헤어진 지 일 년이 지났는데 아직 미련이 남았어요.
It's been a year since we broke up, but I still can't let go.
Word parts
미 not yet+련 refine
Literally 'not yet refined', which doesn't help; learn it as 'can't let go'.
Good to know
Don't confuse with 미련하다 'to be foolish'; 미련이 남다 = to still be hung up on something.