Finalizing naming and such for the 3 classes that will be in alpha - this name was always a bit of a toss up. Demolitionist is long and I don’t think it is actually a word. Demolition connotes blowing things up with explosive though, which I’m not sure Demolisher does as well. Demolisher also seems more generic but it is shorter and has the distinction of actually being a word… We can’t seem to agree among ourselves so, what say you?
Demolitionist all. the. way!
I prefer the generic word since it is actually a name of an occupation/class who demolish things. Demolitionist sounds kinda like an adjective that is describing a Demolisher. Pretty redundant there.
If Demolisher is still not good enough, why not try to find synonyms of the word Demolisher. The only other good word I can come up with is Destroyer.
I can come up with
Annihilator
Eradicator
Iconoclast (my personal favourite)
Demolisher seems so lame.
Demolitionist, is, by the way, a word.
Since we’re playing synonym, Pyrotechnic.
Sappeur. English equivalent would be Pioneer I guess.
Other than that: Demolisher.
Hmm, since none of the skills deal with the destruction of religious or traditional symbols or imagery, I’m not sure this fits. 
While Eradicator looks good, it does not really fit well as a class name, but is good as a character name. Annihilator can fit well with both as a class name and character name. Iconoclast, meh I do not know what to say about it.
Iconoclast, though cool, is not a very fitting name for someone who demolishes material stuff. It would be a very cool classname for Demolisher (or whatever) + Cultist, that’s a perfect fit.
There’s a bunch of other synonyms, as others have said. A few ones that haven’t been named yet; pillager, ransacker, vandal, wrecker. Personally, I prefer Sapper. It’s short, catchy, fits into the era and it doesn’t remind me of bad '90s Schwarzenegger action flicks.
Of the two though, I prefer Demolisher.
Mmmh… i prefer Demolisher, but I m sure we could find some alternatives. English is not my native language so, it s a bit difficult for me 
Maybe something like Pyrotechnician/Pyrotechnist, Engineer, Burner or Powderman ?
See you !
I like Demolitionist, because it brings to mind the image of someone tinkering with explosives and setting charges to collapse buildings.
Demolishers sounds like the name of a brutish giant that smashes things and creates senseless violence without thinking.
The only other suggestion I would offer is the name Grenadier, it has military roots which would fit with the class theme I think. It could also be a name of the combination of two masteries as well.
Also a link: About Grenadiers
Demolitionist
I think originality and creativity go a long way, looking here at another ARPG - Duelist? Shadow? 
Definitely Demolitionist
You could always go with The Exploder! Or The Detonator!
lol jk just go with the Demolitionist,
I like Grenadier, otherwise Demolitionist as it is a word is very specific to what the mastery is about - exploding things.
grenadier sounds awesome; i picked demolitionist
Out those two, Demolitionist. Demolisher sounds like some dude running around with a sledge hammer or something.
Other suggestions:
Grenadier
Engineer (in the army they blow stuff up more than they build )
I actually considered those two but felt that Grenadier was a little too specific, while engineer, some people may not understand the military connotation. Plus, in games with engineer classes, usually they do also fix / build things, along with blowing stuff up. There is no fixing or class-specific building in GD.
Nah, what you are describing is something akin to a Barbarian/Berserker.
Yah, sorry that’s the image it brings to my mind. Demolisher sounds more like someone who’s in construction than someone who is running around lobbing grenades
Demoman: “One crossed wire, one wayward pinch of potassium chlorate, one errant twitch…and kablooie!”
But, since that is not an option, yeah, not demolisher, that class name should be for a morning star, ball and chain specialist. And yes, I sure would like to mix those two masteries.