What would a round white pill with no imprint be identified as?

From Drugs.com

All prescription and over-the-counter (OTC) drugs in the U.S. are required by the FDA to have an imprint code. If your pill has no imprint it could be a vitamin, diet, herbal, or energy pill, or an illicit or foreign drug. It is not possible to accurately identify a pill online without an imprint code.

I suggest you take the pill to a pharmacy for them to dispose of it safely.