In _The Hobbit_ (p. 236 and footnote) we find mentioning of an Orc
chieftain by the name of _Bolg_ son of _Azog_. He is an Orc of the
Misty Mountains, about which Tolkien says that they "had long used
the Westron as their native language" (LR:1131).
As for the name _Bolg_, that could be, in theory, of orkish "proper"
origin (Black Speech) or taken from some Mannish tongue. Given the
geographical position of Bolg's chiefdom, his name might be of
(North-)Germanic origin. That is, Tolkien would use such a word to
represent a Westron word.
If so, Old Icelandic _bolginn_ 'swollen' could be a good starting point.
The shortened form would roughly parallel Orkish _tark_ 'man of
Gondor' < Q. _tarkil_ (ibid.). The meaning may have appealed to
Tolkien, possibly with the by-sense of 'swollen-headed' (cf. French
_gonflé_, German _aufgeblasen_) for the Great Goblin. [The Great
Goblin is described as "a tremendous goblin with a huge head", _The
Hobbit_, p. 60 -- PHW.] Better still, perhaps, we know that Bolg gets
exceedingly angry at Thorin's company and, in his rage, attacks the
Dwarves at the Lonely Mountain. Here fits well the meaning of the
corresponding verb in OE, OS, OHG _belgan_ 'to be angry, rage'.
So maybe Bolg's name is a sort of pun, with Tolkien having something
like 'swollen with rage' in mind.