What is the root for in English?

The root for "in" in English is actually not a single word, but rather a prefix. It's derived from the Old English "in-" which means "in, into, on, upon, at, toward, within, among, by, during, by means of, by reason of, with, against".

Here's how the prefix "in-" works in various words:

* "in" + "side" = "inside": This means being within something.

* "in" + "visible" = "invisible": This means not able to be seen.

* "in" + "valid" = "invalid": This means not valid or legal.

The prefix "in-" can also be used to create negative forms of words:

* "in" + "capable" = "incapable": This means not capable of doing something.

* "in" + "correct" = "incorrect": This means not correct or wrong.

While the prefix "in-" has its roots in Old English, it's a very common prefix in modern English, used in many words across various contexts.