a.

1. 愛虛榮的，自負的，炫耀的
   She is vain and extravagant.

   她既愛虛榮又奢侈。

2. 徒然的，無益的
   They made vain attempts to reach the mountaintop.

   他們幾次徒然嘗試想攀登山頂。

3. 【書】空虛的，無意義的，無價值的

adj.

1. having or showing an excessively high opinion of one's appearance or abilities.
2. producing no result; useless.
   ▸having no likelihood of fulfilment:

   a vain boast.