hair‧piece /ˈheəpiːs $ ˈher-/ noun [countable]
a piece of false hair that you wear on your head to make your own hair look thicker ⇒ wig, toupée

[TahlilGaran] Dictionary of Contemporary English ▲

wig an object covered with artificial hair that you wear on your head:
In England judges still have to wear wigs.
Do you think it's real, or is it wig?
toupée an area of artifical hair, used to cover a bald part of your head:
The singer used to wear a toupée, and then decided to shave all his hair off.
hairpiece a wig or a piece of false hair that you wear on your head to make your own hair look thicker:
Unfortunately the hairpiece didn't quite match the colour of her hair.
extensions long pieces of artificial hair that can be attached to your hair to make it look longer:
I'm thinking of having extensions because my hair gets to a certain length and then becomes so thin that you can see through it.

[TahlilGaran] English Thesaurus ▲