A gallowglass was a mercenary soldier of Irish clan chiefs… originally they came from the Hebrides, apparently, of Celtic-Norwegian origin; they were heavily armed and extraordinarily fearsome.
I always thought the word was derived from ‘gallows’ and understood these were men who escaped the gallows if they fought for their king, an early version of ‘The Dirty Dozen’, die fighting or die hanging…. but I was wrong. I was also under the misapprehension that they were semi zombie-creatures, again, I can find no reference to this when looking up the derivation of the word.
The name is derived from Gaelic, apparently and means foreign fighter, or mercenary. It can be spelt galloglas, or galoglas, as usual with words which come from another language, the transcribed spelling varies. Shakespeare refers to them in Macbeth
Doubtful it stood;
As two spent swimmers, that do cling together
And choke their art. The merciless Macdonwald–
Worthy to be a rebel, for to that
The multiplying villanies of nature
Do swarm upon him–from the western isles
Of kerns and gallowglasses is supplied;
And fortune, on his damned quarrel smiling,
Show’d like a rebel’s whore: but all’s too weak:
For brave Macbeth–well he deserves that name–
Disdaining fortune, with his brandish’d steel,
Which smoked with bloody execution,
Like valour’s minion carved out his passage
Till he faced the slave;
Which ne’er shook hands, nor bade farewell to him,
Till he unseam’d him from the nave to the chaps,
And fix’d his head upon our battlements.
Lois Elsden 