Definition of "sickerly"

My Lord sickerly, / Quoth he, faine would I your pleasure fulfill.

1614, William Browne, The Shepheards Pipe

Awa awaw, sayn yeou this sickerly, or done you but jaum me?

1634, Richard Brome, Thomas Heywood, The Late Lancashire Witches

My gentle bleed […] Right sickerly does plead.

1742, Robert Forbes, Ajax His Speech to the Grecian Knabs