Definition of "highering"

Heaven yield her for it, but in me put force / To weary her ears with one continuous prayer, / Until she let me fly discaged to sweep / In ever-highering eagle-circles up / To the great Sun of Glory, […]

1874, Alfred Tennyson, “Gareth and Lynette”, in Idylls of the King (The Works of Alfred Tennyson; V), cabinet edition, London: Henry S. King & Co., […], page 38