What are words that begin with bi and mean 2?

You're looking for words that start with "bi-" and indicate the number 2. Here are some common examples:

* Binary: A system of numerical notation that uses only two digits, typically 0 and 1.

* Biped: A two-footed animal.

* Bicentennial: A two-hundredth anniversary.

* Biennial: Occurring every two years.

* Bisect: To divide something into two equal parts.

* Bilateral: Affecting or involving two sides.

* Binocular: Relating to or using both eyes.

These words all have the prefix "bi-" which comes from the Latin word "bis" meaning "twice."