Muni is someone who does introspection ( अन्तर्दर्शन ) or who is thoughtful.
According to Shrimad Bhagwadam: Muni is one who is an expert in mental speculation or in thinking (remember मनन् ) or feeling.
Rishi is a title that is given to the one who knows everything about Shastras and the science behind it.
One can call rishis ancient scientists who developed shastras like kundalini yoga and others.
•Maharshi: A rishi who is very great in his spirituality. •Rajarshi: A king who is so spiritual that he is also like a rishi.
•Devarshi ( a deva who is also a rishi) eg: Narada, •Brahmarshi ( a rishi who has seen the supreme Spiritual Truth) eg: Vashishtha, Vishwamitra.
The one with righteous behavior, who is noble and humble. In general a good person.
It refers to a person who has done a lot of penance( तपस्या ) and is eligible to give knowledge to social people.
The one who has given up everything materialistic for the purpose of attaining god.
Yogi or Bhakt - Those who render actual service to the Lord.