Definition of "sware"

He shoke downe all the clothys,And sware horryble othesBefore the face of God, […]

c. 1503–1512, John Skelton, Ware the Hauke; republished in John Scattergood, editor, John Skelton: The Complete English Poems, 1983, page 63, lines 51–53

so I sware to the rose,/"Forever and ever, mine."

1855, Alfred Tennyson, Song from Maud