Gundabad is a mountain in the northern Misty Mountains in the vicinity of where they connect to the Grey Mountains.  It was here that Durin I awoke from where the Vala Aulë placed him to await the advent of the Elves in
Cuiviénen.  During the early ages of the world, the Dwarves of all seven kindreds held regular assemblies of delegates.  For these reasons, the Dwarves held the site in reverence.  At some point, Orcs overran Gundabad and turned it into a stronghold for their own use.  This defilement was a prime factor in why the Dwarves carried such hatred for the Orcs.  They cleared Gundabad of Orcs at least once, during the War of the Dwarves and Orcs, but couldn't not maintain it for a long period of time.

No translation is given for Gundabad, but the first element, gund, can be seen from Felak-gundu.  Here it appears without the -u ending, so it appears to be in the singular, nominative form rather than accusative.  This is the same template as Khuzd: CuCC.  It means an "excavated tunnel", probably of an artificial nature as noted in the section on Felak-gundu.  It could be that Aulë created such a delving, but since much of his other work seems to be more natural (he created the Dwarves, after all!), it seems probable that Durin awoke in a natural cave.  The Dwarves may then have expanded the caverns in the same manner that they Petty-Dwarves did at Nuluk-khizdîn (although one might assume it was done with more skill than the Petty-Dwarves).

Gund is "underground, excavated hall", the same as Felak-gundu, but here it is singular, nominative, composition.

The meaning of abad is completely unknown .
I could see it meaning something like "birth" or "awakening", but only Durin awoke here, and I'm not sure he would have named it right away. However, because this is where the Dwarven tribes held their summits, I think a more likely interpretation is "meeting". Also, this is where the Misty Mountains and the Grey Mountains attach, so it makes sense in that view as well. The only thing that gives me a little pause is that the CaCaC pattern, which is attested more for adjectives in narag "black" and zahar "hollow".  '-B-D would be a verbal root "to meet", and gerunds seem to have a common pattern of CaCiC from gabil "great, mighty, large" and gamil "aging, oldness".  However, none of that exludes the possibility that CaCaC could be used as a gerund pattern, or it could be some kind of infinitive.  I don't think it's a huge problem though, and we can stick with the interpretation.  It is, in any event, a hypothetical guess.

Abad could then be, speculatively, "meeting" and singular, nominative, indefinite.

Gundabad would be a construct compound word, "Hall of Meeting", and have a noun-noun or noun-verb word order.

The Peoples of Middle-earth, pg 301