덧없이 지나가다 · 덧없다 (adj.) · 덧없는 인생
fleetingly, transiently, in vain
Example
젊은 시절이 덧없이 지나가 버렸어요.
My youth passed by all too fleetingly.
Word parts
덧 is an old word for a brief moment; compare 어느덧 'before you know it'.
Good to know
Pronounced [더덥씨]; 덧없는 인생 'fleeting life' is a classic phrase.