1) A verb meaning to cleave or cut.
1617 thornes … had bene ether stubbed or sleven, Brandsby. The noun is also recorded: 1617 some slyvings of yonge oaks from ould stovens, Brandsby. The OED has a reference from 1688 to ‘A Sliven, Shivered, or Cloven tree’.
2) The verb meant to slip on a garment such as a hood.
Here it is linked more unusually with clothing for the legs: 1518 I give to Robert ... a par of Whit Slyvyng hose, Barkston
1558 I bequeath to Robert Reame a paire of old slyve hose, Whitkirk.