...popup modal widget that shows information about different terms mentioned in blogs, when hovering over a term...
Am I reading this right? You're saying, a modal popup happens when someone simply hovers over a term? This sounds suspiciously like those ads you get from double underlined words in blogs and news sites.
If this is related to ads, I have no advice for you. You're going to have to get it all from user testing. There's no standard/easy way that you can interrupt a person who's performing some task they want to do, and force them to read or become interested in something you want them to. And, I'd venture to guess that all popups related to ads are a poor solution.
...people hate popups, no matter what's in them.
I wouldn't say that. People just hate popups that warn them about something they were already committed to doing. (e.g. Are you sure you want to quit? Are you sure you want to delete this file? etc.) This leads back to "Never use a warning, when what you mean is undo."
Popups are perfectly fine when there's a valid reason. For instance, when copying files in Windows Vista/7 from one folder to another. If it reaches a conflict with a file of the same name, there is a popup. The popup gives you several options to how to resolve the conflict, as well as a way to avoid future popups by repeating your choice for future conflicts.
In computing, it's all about flow. You don't want to break a person's flow unless you absolutely have to.