Question: to do something in vain?
Answer: Vain. This is an adjective which means 'not achieving the desired outcome', 'futile', 'unsuccessful', 'lacking substance or worth', 'hollow' and 'fruitless'. As an adjective, it also means 'showing undue pride and preoccupation in your own appearance'. It is also used in the idiomatic phrase 'to do something in vain'.