The legality is likely to be an issue if the name has been trademarked but others here would be able to give you more feedback on that. A bigger concern should probably be confusion as you would immediately find yourself potentially losing focus on your typeface in favour of the other one available.

I remember a comment made elsewhere on this site about the possibility of naming typefaces after Autechre track names and I think 65daysofstatic and Godspeed You! Black Emperor would be fertile territory for similar inspiration, just in the field of music; literature, art or a copy of the OED (or perhaps rather ADL) would prove just as inspirational. I am not suggesting that you should abandon your considered name but there are so many unexplored possibilities and something unique is likely to be beneficial in drawing attention to your font.

In the case of nouvelle vague the fonts are named after a film style. I think there is generally a difference between copying original names and copying names that borrow from something else, especially if your inspiration doesn't come from the other font. Similarly, one could call a font Flutter or Tilapia (which are tracks by Autechre) without any problems, but I'd be more cautious with calling it Maphive 6.1.
Karl Stange, I'm curious to know what track name's this person was thinking of. Nothing particularly fitting comes to mind. (Except maybe The Egg as an alt. name for Hobo.)

Thijs, I think it was posited as a general idea, to try and escape the typical conventions of font naming. I do not know if they had specific tracks in mind.

From a casual glance at a track listing, "Tankakern", "Ipacial" (partial) and "Augmatic Disport" jump out as good candidates. I liked the idea of "East Hastings" or "Moya" from Godspeed and "Tiger Girl" and "Retreat, Retreat" from 65daysofstatic, but more from an arbitrary impressionistic point of view, rather than relating to aspects of typography or fonts.

I had "Voltage" in mind.
http://letterpressfonts.com/voltage-normal-font-p-1600.html

I don't think that would be a problem at all. Maybe, for uniqueness, you could add something to the name.

BTW you url letterpressfonts doesn't work for me.

Consider that the EU authorship legislation grants the author’s rights even without registering anything (in the US it isn't the case), if precedence can be proven.
Adding something to your name would save you from any possible issue.

Trademark doesn't need to be registered and can be based solely on established usage in the marketplace, and note that marketplace in this instance doesn't imply commercial: a free font name can still be considered a trademark, since the purpose of trademarks is to avoid confusion of products and providers in the marketplace. So if you introduce a product with the same name into the marketplace, that may be considered trademark violation, regardless of whether the other product is commercial or free. Whether the maker of the free font would take the time and expense to defend the trademark by bringing a lawsuit against you is another matter. Perhaps more to the point though is that you might have trouble claiming the trademark for yourself, since there is established prior use in the marketplace.

As a general rule: when in doubt about such a question ask a lawyer, not a bunch of typographers on the interwebs.

[Disclaimer: I am not a lawyer, and the above is not offered as legal advice.]

Karl’s advice is sound. Forget about legality: why muddy the water and create confusion for potential buyers? I know from personal experience—I recycled one of my own freeware font names and used it for a commercial release—that the process can produce a few unhappy campers.

A quick Google search suggests that the name “Megawatt” isn’t being currently used for a typeface; use it—or something like it—instead. Same basic idea, lots more punch…