Q:

Is it legal to use other game's title word in my game's name?

Is it legal to use e.g. the word "Fortress" in my game’s title? 
There is a game called Team Fortress and I think it’s trademarked. I’m thinking of replacing the word "Team" with another word and using that name in my game (with an intent to make money). 
Would I get in trouble?

A:

Usual disclaimer: I am not a lawyer and in this site questions about these issues have to be always taken as ideas, thoughts or experiences, never as technical advice.
That said, it's good that in your question you use both the tags "copyright" and "trademark", because indeed your question in the end touches the difference between these two. I say that because a game's title can be trademarked, while the asset's of games can be copyrighted. At the same time, the concept or the gameplay of a game is a more difficult matter. For a nice quick guide/discussion to that, including some points that are very directly related to your question, see the article "Video Games and the law: Copyright, Trademark and Intellectual Property".

Now, let me briefly address particular issues raised by your question.
First of all, certainly words in themselves are not trademarked per se. Second, if you take the title of a game and change it enough, you certainly can be safe from issues regarding the trademark of the original game's title. The problem is that how much is "enough" is something that can't be determined a priori. Therefore, there is always risk (and consider that the problem of being sued is not only loosing, but even before that, wasting time and resources on the matter).
However, your main problem does not seem to even be the infringement of the trademark of another game's title, but rather you being afraid of copyright infringement since by your comment to other answers you seem to plan to fully copy the gameplay of a copyrighted game and just modify your version's title to avoid having your gameplay-copy from being sued.
Here things are more dubious. On the one hand, the US Copyright office says that:

Copyright does not protect the idea for a game, its name or title, or the method or methods for playing it. Nor does copyright protect any idea, system, method, device, or trademark material involved in developing, merchandising, or playing a game. Once a game has been made public, nothing in the copyright law prevents others from developing another game based on similar principles. Copyright protects only the particular manner of an author’s expression in literary, artistic, or musical form.

On the other hand, this is a bit too vague for making one feel safe. In fact, the interpretations at the Courts have been diverging quite bit. There is an excellent article on Gamasutra, from 2013, that discusses that: "Clone Wars: The Five Most Important Cases Every Game Developer Should Know".
Therefore, copying the title and copying the whole game mechanics are two different things that are not necessarily related. I mean, even if your title isn't considered to be infringing the trademark of another game's title, your game fully copying another game's gameplay can put you into trouble. Even if your game's title is 100% different (but of course if the title is also similar, it will be used as additional evidence of you desiring fully copying the copyrighted game).
And when I say that it can put you into trouble, I mean the following. Although game ideas and game concepts in general can not be copyrighted, the problem is two-folded:
a) if your game calls enough attention from the original game's company, considering the law is a bit dubious here, they might try their luck and sue you because fighting at the courts is proportionally much more of a burden for you than for a big company.
b) again, since things definitions and rules are a bit too vague in the case of gameplay, game concepts and game ideas, you always incur in the risk of courts deciding that you went too far and really copied the original game just disguising that. After putting a lot of your time and resources on making the game, just that risk is often too big since all your efforts would be at a loss.
Hope it helps!

A:

No, it's not illegal to use words from another trademark. Police won't visit you, and you won't have to go to jail, even if you outright use the same trademark.
However, holders of any trademark can decide to sue you, either to make you stop using the name, to make you give them a share of the income from the game, to make you acquire a license from them for further use of the name, to compensate them for damage done to their brand, or any combination of those. 
Their chances to win the case increase if their case is stronger and/or if they have more lawyers. The case for them is strongest if the name is very similar to your trademark (e.g. squad fortress), the trademarked object is similar (e.g. you make a capture the flag 3D
 shooter with comic-like graphics), and the 2 products actually compete with each other. Further details depend on jurisdiction.
Once they win the case and you refuse to pay them and/or the court, you might be doing something illegal and should worry about police and jail.
Cases where anyone sues you do not have to have any merit at all to succeed. As soon as the cost for defending is significantly higher than the cost of the settlement, most people settle. Case in point: http://www.pcgamer.com/rebellion-sues-stardock-for-using-its-name-in-sins-of-a-solar-empire-rebellion.

A:

I think too much emphasis is made on legal use of trademark. The bottom line is that you may be sued for just about anything. The best way not to be sued is for your game not to become popular. If Minecraft was just as unsuccessful as the games it copied its gameplay from, then it would probably not have problems from Bethesdas paranoia. If you need legal advice go for a lawyer, but keep in mind that the bigger blip you are on the radar the higher likelihood of being sued for just about anything.

