I think that Connacht, Callieach, Cath Bruig... and other names are gaelic or derived from it. Judge yourself:
cath
battle, Irish, Old Irish cath, Welsh cad, Old Welsh cat, Cornish cas, Gaulish catu-; Old High German hadu-, fight, Anglo-Saxon heađo-, German hader, contention; Sanskrit çatru, enemy; Greek @Gkótos, wrath.
bruigh
large house, a tumulus, so Irish, Early Irish brug, mrug, land, holding, mark, Welsh bro, country, region, land, Cym-mro, a Welshman, pl. Cymmry (*com-mroges), Breton bro, country, Gaulish Brogi-: *mrogi (for Gadelic); Latin margo; Gothic marka, border-country, Anglo-Saxon mearc, border, English mark, march.
So Cath Bruig might mean house of battle or tumulus of a battle.
this page offers gaelic dictionaries online
http://www.ceantar.org/Dicts/index.html