/veɪn; ven/
adj (-er, -est)
1 having too high an opinion of one's looks, abilities, etc; conceited （对自己的才、貌等）自视过高的; 自负的.
2 [attrib 作定语] (esp rhet 尤作修辞) having no value or significance 无价值的; 无意义的
*vain promises, triumphs, pleasures 空头的许诺、虚无的胜利、空欢喜.
3 [usu attrib 通常作定语] useless or futile 无用的; 无益的; 无效的; 徒劳的
*a vain attempt 劳而无功的努力
* in the vain hope of persuading him 指望说服他而徒费口舌.
4 (idm 习语) in `vain
(a) with no result; uselessly 无结果地; 徒然
*try in vain to sleep 怎么也睡不着.
(b) fruitless or useless 无效果的; 无用的
*All our work was in vain. 我们的工作全都白干了. take sb's name in vain => name1.

adj
[Date: 1300-1400; Language: Old French;Origin:Latin vanus 'empty, vain']
someone who is vain is too proud of their good looks, abilities, or position - used to show disapproval
= conceited
　Men can be just as vain as women.
see usage noteproud
in vain
a) without success in spite of your efforts
　Police searched in vain for the missing gunman.
b) without purpose or without positive results
　Altman swore that his son's death would not be in vain.
→take sb's name in vainatname¹ (12)
a vain attempt, hope or search fails to achieve the result you wanted
vain attempt/effort/bid
　The young mother died in a vain attempt to save her drowning son.
vain threat/promise etc
literary a threat, promise etc that is not worrying because the person cannot do what they say they will
>vainlyadv
　The instructor struggled vainly to open his parachute.