Oh okay, noting the word religious in the definition of religion is defining the word with the word. It is as you say circular reasoning to do so
according to dictionary.com the word religious means
"of, pertaining to, or concerned with religion: a religious holiday."
pretty much something or someone that has something to do with religion
okay, what is religion?
Religion - Definition and More from the Free Merriam-Webster Dictionary
: a cause, principle, or system of beliefs held to with ardor and faith
a system of beliefs
What is ardor? ardor means loyalty
What is faith? firm belief in something for which there is no proof
What is an opinion?
belief stronger than impression and less strong than positive knowledge
What is a thought? something (as
an opinion or belief) in the mind <he spoke his thoughts freely>
Religion - Definition and More from the Free Merriam-Webster Dictionary
Wow, so long as someone has an opinion on something they are religious.