Look for the Catholic definition...
That line of thinking alone should let you know the Church is evil, and they're infecting you with their evil. You should be looking at God's definition of sin, it's the only one that matters.
You know that many words have different meanings, right? If you look at entries in the dictionary there will be words and the meanings enumerated. Which means at times a word will not mean the same in all aspects depending on how it's used or which field (science, art, business, etc.) it is used. So why is telling you to look for the Catholic definition evil for you when it's exactly the same thing as looking at a dictionary and searching for the religious definition?
God's definition of sin indeed is often overlooked by people who don't do an Examination of Conscience. I highly suggest you also find one online that you can use when confessing directly to God (because most Christians don't have the sacrament of confession). Plenty of that on the web, choose whichever you prefer. 😁 We can always ask God for guidance on which one to choose. Let's follow whatever is His will for us.