What are words that have the prefix gn?

You're right, there aren't many common words in English that start with "gn". In fact, there are only a handful, and most are related to the act of knowing or understanding:

* Gnat: A small, biting fly.

* Gnaw: To bite or chew something persistently.

* Gnome: A small, mythical being that lives underground.

* Gnostic: Relating to knowledge, especially mystical knowledge.

* Gnomic: Relating to gnomes or having a concise and mysterious quality.

* Gnomish: Relating to gnomes or having a small, mischievous quality.

There are some less common words with "gn" as well, but they are more obscure and less frequently used.