Modern English is a rather strange language. It is a basically a train wreck between Anglo Saxon (also known as Old English), Old Norse and Norman French
Here’s an example
I am mad (mad comes from Old English ġemǣdd)
I am angry (angry comes from Old Norse angr)
I am agitated (agitate comes from Latin agitatus)
These words all generally mean the same thing with with some nuance to their meanings.
Old English was an inflectional language. This means that it used inflections on verbs and endings on nouns