What is antonym for napkin?

There isn't a direct antonym for "napkin" in the sense of a piece of cloth or paper used to wipe the mouth or hands.

However, depending on the context, you could consider these alternatives:

If referring to its purpose:

* Dishcloth: for washing dishes

* Towel: for drying hands or body

* Sponge: for absorbing liquids

If referring to its material:

* Cloth: a broader term for fabric

* Paper: a broader term for material made from trees

It's important to understand the context and the specific aspect you are looking for an opposite of.