Vain (Adjective) = useless, Conceited
Synonyms: Futile, Pointless, Worthless, Conceited, Self-admiring
Example: All his efforts are going vain.
Vein (Noun) = Blood vessels carrying oxygen-depleted blood towards the heart.
A fracture in rock containing a deposit of minerals or ore.
Synonyms: Accumulation, Deposit Layer, Stratum, Stratification,
Example: The injection was given in the vein.