From "Collins Encyclopaedia of Scotland", edited by John and Julia Keay, 1994.

"The etymology of the name of Scotland's largest city is warmly disputed. It's derivation is surely Celtic and probably Gaelic; but with anglicized spellings varying widely from "glas-chu" to "glas-cun", the component words are uncertain, let alone their precise meaning. In the heyday of 19th cent. industrialisation "glas" was taken to mean "grey", leading to such seemingly appropriate translations as "the grey blacksmith" ("gow" suggesting "gobha", a smith)or "the grey hound ferry" ("cu", a dog).

Currently the favoured derivations are more pastoral and cultural with "glas" taken to indicate "green" or a "church". Hence the popular "dear green place", "green hollow", "dear stream", "green cloister", "dear cloister", "church within the enclosed space", "church of Cun(tigernus) [Kentigern], etc".

A gift to the imagemakers, such uncertainty also accords well with the City's occasional need to reinvent itself."

That seems to cover most bases but it's a long, long way from Garryowen to here!