Definition of "sleekit"

‘Damn your impudence, Duror,’ he said. ‘You're a sleekit one all right.’

1955, Robin Jenkins, The Cone-Gatherers, Canongate, published 2012, page 19

They were not sleakit and did not knife ye, that was one thing. They were not fly men cheaters.

2008, James Kelman, Kieron Smith, Boy, Penguin, published 2009, page 390