a mermaid tail
A mermaid tail is a fake tail you wear to look like a mermaid. It's made of stuff like swimsuit material or rubber. It's just a costume, but some people think it's magic.
My friend wore a mermaid tail to a party and everyone thought she was a real mermaid.
I wore a mermaid tail to the beach and looked like a sea monster.
My dog tried to eat my mermaid tail and now he thinks I'm a monster.