It comes from the Latin word *alter*, meaning "the other of two".
This root is found in many English words, such as:
* Alter: to change or modify something.
* Alternate: to change back and forth.
* Alteration: a change or modification.
* Alternative: a different possibility or choice.
* Altruism: selfless concern for the well-being of others.
The meaning of "other" or "different" is reflected in these words. It highlights the concept of something being changed, modified, or replaced by something else.