A monocle is a small, round piece of glass that someone wears in one eye to help them see better.
Monocles are old-fashioned and can make people think of fancy, rich people from a long time ago.
Examples:
The man with the monocle looks very fancy.
I found a monocle in my grandfather's old things.
She wears a monocle to read better.
The cat tried to wear the monocle, but it didn't work.
In the movie, the king always has a monocle in his eye.
I want to try on the monocle and look fancy too.