Definition of "eyass"

When Roland Græme was a youth about seventeen years of age, he chanced one summer morning to descend to the mew in which Sir Halbert Glendinning kept his hawks, in order to superintend the training of an eyass, or young hawk, which he himself, at the imminent risk of neck and limbs, had taken from a celebrated eyrie in the neighbourhood, called Gledscraig.

1820, [Walter Scott], chapter IV, in The Abbot. […], volume I, Edinburgh: […] [James Ballantyne & Co.] for Longman, Hurst, Rees, Orme, and Brown, […]; and for Archibald Constable and Company, and John Ballantyne, […], page 82