The words vane, vein and vain are pronounced the same but each has a different meaning. This article explains how each word is used in English.
vane

Vane is a countable noun.
A weather vane is a metal object on the roof of a building which turns round as the wind blows. It is used to show the direction of the wind.
He has now started repainting the weather vane.
vein

Vein is a countable noun.
Your veins are the thin tubes in your body through which your blood flows towards your heart.
Many veins are found just under the skin.
vain

Vain is an adjective.
A vain attempt or action is one that fails to achieve what was intended.
The drafting committee worked through the night in a vain attempt to finish on schedule.
I was singing in a vain effort to cheer him up
If you describe someone as vain, you are critical of their extreme pride in their own beauty, intelligence, or other good qualities.
I think he is shallow, vain and untrustworthy.
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