adj. 25B6; adjective
he was vain about his looks : CONCEITED, narcissistic, self-loving, in love with oneself, self-admiring, self-regarding, egotistic, egotistical; proud, arrogant, boastful, cocky, immodest, swaggering; informal big-headed; poetic/literary vainglorious.
a vain attempt : FUTILE, useless, pointless, to no purpose, in vain; ineffective, ineffectual, inefficacious, impotent, unavailing, to no avail, fruitless, profitless, unproductive, unsuccessful, failed, abortive, for nothing; thwarted, frustrated, foiled; archaic bootless.
modest, successful.
25A0; in vain
they tried in vain to save him : UNSUCCESSFULLY, without success, to no avail, to no purpose, fruitlessly.
his efforts were in vain. : See vain sense 2.