What is that latin root word for computer?

There isn't a single Latin root word for "computer." The word "computer" itself is relatively new, first appearing in the 17th century. However, we can trace some of its constituent parts back to Latin:

* "Compute": This word derives from the Latin verb "computare," meaning "to reckon, calculate, or count." This is the root of "computer" in the sense of a machine that performs calculations.

* "-er": This suffix is common in English, indicating an agent or person who performs the action of the verb. So, "computer" is literally someone who "computes."

Therefore, while there isn't one specific Latin root for the entire word "computer," the roots "computare" and "-er" play a crucial role in its formation and meaning.