What is the base part of word?

The "base" part of a word is called the root. It's the core meaning of the word, and it's often the part that doesn't change when you add prefixes or suffixes.

For example:

* "Happy" is the root of "unhappy", "happiness", and "happily".

* "Write" is the root of "rewrite", "writer", and "writing".

The root is the foundation of a word, and understanding it can help you to understand the meaning of related words.