antonyms for eccentric

    common.
    conventional.
    familiar.
    normal.

Having cancer is the opposite of being healthy, but the opposite of healthy is being sick rather than just having cancer.

Aka, someone that’s homicidal is abnormal but not necessarily eccentric.

having cancer is not the opposite of healthy, several aquatic creatures live just fine / "healthy" with cancer

BS. Cancer is different than a simple tumor. It is by definition unhealthy.

Ok you’re right after further researching, I had mixed up a part which led to the incorrect notion.

Having cancer is being sick...

But being sick doesn’t always mean having cancer.

"When I was young, I was called a rugged individualist. When I was in my 50s I was considered eccentric. Here I am, doing and saying the same thing that I did then, and I'm labeled senile."

https://www.imdb.com/title/tt0079384/characters/nm0122675

touché.