Question

What is the suffix or ending in argument and what does this suffix mean?

Answer 1

The suffix is -ment. This suffix means the action of doing something.

Answer 2

A suffix is a bit of speech that gets attached at the end of a word to modify it or to make it into a related word. For example, you can attach -er to the end of a great many verbs to get a word meaning "person who does X"