1 proud, conceited, haughty, arrogant, boastful, egotistical, cocky, self-important, vainglorious, narcissistic, Colloq big-headed, swell-headed, stuck-up, swollen-headed:
They are so vain that they have mirrors in every room.
2 worthless, profitless, bootless, pointless, unsuccessful, empty, futile, useless, unavailing, unproductive, fruitless, ineffective, abortive:
Peter sent Carol flowers every day in a vain attempt to win her back.
3 in vain.
(a) vainly, futilely, unsuccessfully, fruitlessly, bootlessly:
In vain, we sought the help of the police.
(b) irreverently, blasphemously, disrespectfully, improperly:
Despite his mother's admonitions, he continues to take the Lord's name in vain.