Can somebody define metonymy?

Well its a noun.

the substitution of the name of an attribute or adjunct for that of the thing meant, for example suit for business executive, or the track for horse racing.

I looked it up and it says that it means the substitution of the name of an attribute for that of the thing meant, for example suit for business executive, track of horse racing.

Also it is a noun. Basically, what the person above said.