Meaning of “vain” - Learner’s Dictionary

vain

adjective uk us /veɪn/
in vain

without any success:

I tried in vain to start a conversation.
vain attempt/effort/hope

an attempt/effort, etc that does not have the result you want

too interested in your own appearance and thinking you are very attractive

vainly adverb

(Definition of “vain” from the Cambridge Learner’s Dictionary © Cambridge University Press)