힘들어요 · 힘들었어요 · 힘든 (+noun) (ㄹ drops)
hard, tough, tiring; tired
Example
회사 일이 많아서 요즘 정말 힘들어요.
I have a lot of work these days, so things are really tough.
Word parts
힘 (strength) + 들다 (to take, to be needed): 'takes a lot of strength.'
Good to know
힘들다 is about effort or exhaustion; 어렵다 is about something being hard to understand or solve.