What is Vain ?
Vain is (adj) 1. which does not succeed She went to the pub in the vain hope of finding him there. 2. in vain without any success We waited in vain for a bus and had to walk home. he did not die in vain his death had an immense moral effect on people 3. very proud of your appearance, clothes, achievements, etc. He’s very vain, and is always combing his hair. (NOTE: vainer vainest. Do not confuse with vein.)
source: Easier English, Student Dictionary Upper Intermediate Level