It's a very common root in English, appearing in words like:
* Polyglot: A person who knows and is able to use several languages.
* Polytheism: The belief in or worship of more than one god.
* Polygon: A plane figure with at least three straight sides and angles.
* Polysaccharide: A carbohydrate whose molecules consist of many sugar units.
The root "poly" often indicates multiplicity or abundance.