So let's say I picked a name for my game, made some progress on it, and then later find that another work is using the same or basically the same title. But I really like the title, and wonder if I can get away with using it.

What exactly are the legal restrictions for a title, (particular for a game)?
In all honesty, there are so many creative works in this world that it it easy to come up with a title that very similar or even identical to one that someone is using. Books, movies, blogs, comics, fiction, products… There are millions of people out there trying to come up with their own thing; it's nearly impossible to come up with a decent title that doesn't sound like something that someone has used somewhere. Surely there must be limits, but what are they?

Obviously I don't want to encroach on a major brand, and I should be observant to any trademarks. But what about works from other media that are using a same or similar name?

I'm really interested in some general knowledge, but since I know someone is going to ask for an example: A name I was considering for my game was “Ruby's Quest.” A google search reveals that someone made a movie with that name seven years ago. There is almost no information abut it because it's pretty obscure, but it still exists. But it's also not a video game. Another title I was considering was “Ruby's Legacy” and there is a book with that name, a sequel it seems. Not very famous, not a video game, and not the headline of a series.
Am I able to skirt around titles like those because it's a different medium? Or because no one has heard of them? Would have to do something like add a subtitle like “Ruby's Quest: The Dragon Estate” or would that still be incurring problems?
I could keep going, keep trying other variants, but at some point I have to pick something, and it's going to have been used in some form somewhere or sound like something someone has used, even if its some blog that hasn't been updated in fifteen years or a chapter title in some book that's been out of print for a century or someone's smutty fanfic that they don't even have the legal right to or some weird BS like that.

I'm not set on these titles, but I need to know what I am allowed to do. Where does this end? At what point am I able to use a title?

From my past experience, this is the worst place to be asking this sort of question. Unless you want a wrong answer.

Anyone that gives a correct answer is attacked with Dunning-Kruger experts on copyright/trademark issues.

A lawyer friend of mine once said, “If you ever have to ask "will this get me in trouble," and you don't want to pay an attorney to find out, you shouldn't do it. Simple. Remember-- Just because you might have a DEFENSE doesn't mean you can't get SUED.”

Obligatory link: https://sloperama.com/advice/faq61.html​​ - but don't read it. It's very annoying, if I do say so myself. But it goes into detail about why you're taking a risk using that title, thus it's all about your risk-taking comfort level. What's the worst that can happen? You can get a lawyerly letter telling you to take your game down. It's unlikely you'll find yourself in court (unless you ignore the letter or try to fight it). Better to change your title now.

While purely anecdotally, I also want to point to the recent case of the publisher “Take Two” suing a lot of different brands with a similar name - for example, the game “It Takes Two”, or the “Take Two” Axethrowing-shop somewhere in america. So yeah, you really don't want to push this if you don't want to get sued - you can even get in trouble if you don't do anything wrong in the first place, as you can see.

Do you want to know if it's legal or do you want to know if you'll get sued? Because those are very different questions.

People use names that have been previously used all the time, and they usually get away with it. Reusing a name is not illegal per se. Check out https://en.wikipedia.org/wiki/Legacy​ and you will see a long list of different media all called “Legacy” - and that's just the notable ones on that page. On the other hand, people get sued for stupid reasons all the time. Check out the Edge Games lawsuits, for example. And reusing a trademarked name is worse than reusing a name that's too generic to trademark.

If you release anything at all, regardless of the name, there is a small but nonzero chance that you will get sued. There is no way to quantify this probability. You probably won't get sued even if you pick a name that's an obvious trademark violation, and there is no guarantee that picking a previously unused name won't get you sued. But if you have to ask, then it's probably safer not to do it.

Tom Sloper said:

Better to change your title now.

I am changing the title, honestly. (Or rather, seriously looking for a better one.) But the truth remains that no matter what I pick, it's going to somewhat similar to something.

So what I'm really trying to figure out is: what's a good measure? What becomes risky?
And while these things are impossible to quantify, there are still plenty of hard examples. “Ion Maiden” got a cease-and-desist order, but Capcom made a villain named “Aqua Man” and didn't. Most of this comes down to the companies involved, but there's still differences in how they were using a name/title.

Probably the most helpful thing to know is as many incidents as possible where action was and was not taken.

Juliean said:

While purely anecdotally, I also want to point to the recent case of the publisher “Take Two” suing a lot of different brands with a similar name - for example, the game “It Takes Two”, or the “Take Two” Axethrowing-shop somewhere in america. So yeah, you really don't want to push this if you don't want to get sued - you can even get in trouble if you don't do anything wrong in the first place, as you can see.

Eh, that still doesn't quite as absurd as Edge Games, let alone King Games.

Marscaleb said:
what's a good measure? What becomes risky?

That's so cute. You still think there's an answer to that! The measure is YOU. Your comfort level with risk. Weigh the possible ramifications of getting a cease-and-desist letter a year after you've released your game and done a bunch of marketing, social media, gotten a web domain, all that stuff. If you are willing to risk it, go right ahead. Don't forget: “If you ever have to ask "will this get me in trouble," and you don't want to pay an attorney to find out, you shouldn't do it. Simple.” That's the measure.

There's a clear violation if it has an active trademark and is in active use. It is lower risk if it has been dead for decades. But regardless of what name you choose, the risk of lawsuit is not zero. It can never be reduced to zero risk.