Well, I don’t mean to be rude, but I think both are kinda lackluster in the creativity department.
Here’s a bunch of other words that have the same level of creativity (or lack thereof);
Destroyer, annihilator, eraser, terminator, exterminator, destructor, destructionist, vanquisher, crusher, executioner, eradicator… seeing a pattern here?
@MadWasp, just my opinion but I don’t really see any of those ideas working.
As for sapper I also don’t think it quite feels right to me. I just get the idea of someone laying/disarming mines. Further definitions also adds bridge-building, demolitions, field defenses, general construction, road/airfield construction/repair.
I kinda like that their is no available description for Demolitionist. To me it just sounds like a professional soldier who uses explosive devices to kill his or her enemies.
Perhaps crate should just make up a word using parts of words so we get the idea as to what it is.
Here are some terrible suggestions for fun.
-Expletonator (explode + detonate = something like terminator but cheesier)
-Erdisaze (erupt + discharge + blaze)
Lawlz.
I don’t like Demolitionist at all. Doesn’t flow off ones tongue.
I’d prefer one of these Brigand(maybe my fave, hope you can use it on another class if not this), Despoiler, Eradicator, Exterminator, Hooligan, Obliterater, Pillager, Ransacker, Razer, Skirmisher, Vandal(another fave) or Wrecker.
Other class names I like are Footpad and Fingersmith.
All shall fear the HOOLIGAN!
Lol… yea no.
On a sarcastic note: how about Terrorist? Although it might not be a good idea with hardcore.
Peacemaker maybe? 
Another good term I run into is Ruiner. And Devastator mentioned above is also sound very good.
I can actually imagine that as a dual mastery term for the Gunslinger mastery + something else. 
Peacemaker was the name of a popular Wild West revolver after all.
Gunslinger + Diplomat maybe? 
That’s what I was keep in mind naming it like this
For the last time, Demolitionist IS A WORD. Look it up.
Now that I think about it, it actually makes sense having Demolitionist over Demolisher since we got Occultist has the other class name. It would not make sense to have Occulter over Occultist.
Real life example: I am into science, thus I am a crazy scientist. :rolleyes:
Though, I still think we should have both since:
Demolisher : The occupation/class
Demolitionist : An individual that demolish things for a living
Demolish: verb
Demolishing: The act of demolish at the moment
I still made the right choice since Demolisher is a class, NOT a person in that class. When I pick the class, Demolisher, I become a Demolitionist. In the character screen, lets say the inventory, the title of my class should be Demolitionist, but the mastery/class should be called Demolisher.
English is always tricky at times, even for a native speaker as myself.
Both Demolisher and Demolitionist are related to people. Like what you said about scientist, Demolish-er- can also be like firefight-er-.
Here is an idea: Have Demolisher as the class/mastery and like Titan’s Quest Demolitionist would be when you JUST choose Demolisher before choosing your second class/mastery. Compensate in allowing both words participate in the overall solution.
So this.
Mastery: Demolisher
Having Demolisher as your first Mastery makes you a Demolitionist.
Choosing a second Mastery will obviously take away Demolitionist as you’ll become a hybrid of two Mastery’s. Perhaps Crate can allow players to ignore taking a second mastery and have the ability to add more points to the Demolisher mastery and the passives which give more stats (so 2 mastery’s would mean capping the amount of stats you can put into each while choosing to stay with 1 mastery means you can put more points into the stats which the maximum would be doubled).
Having a combination of Demolisher and say… Arcanist. You’d get something like Devastator (suggesting a ton of explosive energy via bombs/arcane magic).
Having a combination of Demolisher and Combat you could get something like Grenadier which suggests the combination of explosions and military attacks or something.
Just an idea building off of you idea, JohnNamikaze.
John’s thinking sounds interesting to me.
I noticed that in Marvel Heroes there is an opponent that’s called Demolitionist and looks like the bomb squad guys.
I am glad actually, since my idea sounded kinda awkward the way how I posted it.
I guess we’ll only be seeing this classname for a very short early part of the game. I’m actually more interested in the class combination names
Demolisher if it is more melee centered, Demolitionist if it is more spell based.
Bombardier.
I know this may not be related to the Demolisher/Demolitionist discussion, but if there is ever a “Gunslinger” class implemented, I would love to see its combination name with Demolition be “Desperado” 
why is everyone trying to make demolisher work? i think the vote speaks for itself.