Ad hominem does not just mean insult or negative opinion. That is not why it is typically considered a fallacy.
The dictionary link acknowledges the etymology and, in interpreting both the older use and newer use of the word, still describes them within a "debate" or "argument". Even the first definition in appealing to feelings is given context as an argument. There is a reason why every other source you can look at is going to refer to ad-hominem within the context of an argument or a debate tactic.
If you want to simply conflate ad hominem with insult, then it's your prerogative but then we have to remove all the negative connotations about it being fallacious and so on in it's common and understood usage when you say it to someone.
If you want to take this a layer further:
JOE: He is attempting to discredit my character as I am a lefty
JOE: already showed you that I was correct in using ad-hominem to describe what he did
You linked a dictionary definition in your defense that says, "appealing to feelings or prejudices rather than intellect" ------> which does not imply "discrediting character" at all.
In fact, taking an ad-homimen to be, "discrediting character" would be referencing its etymology and usage as an argumentive style or debate tactic.
So which one is it?
You just argued it was an ad-hominem because he, "discredited" your character but then you defended your use of ad-hominem as being outside of an argument context by a definition that has doesn't inherently imply anything about "discrediting your character".