Kern are mentioned in Shakespeare’s Macbeth (Acts I and V):
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;
Mark, king of Scotland, mark:
No sooner justice had with valour arm’d
Compell’d these skipping kerns to trust their heels,
But the Norweyan lord surveying vantage,
With furbish’d arms and new supplies of men
Began a fresh assault.
I cannot strike at wretched kerns, whose arms
Are hired to bear their staves: either thou, Macbeth,
Or else my sword with an unbatter’d edge
I sheathe again undeeded.