1) A water-filled depression or shallow area between two stretches of rising ground.
c.1270 a Waterslakgille usque ad fossum, Langdale
1329 ‘the place called Watirslack’
1331 ‘and one rood lies at le Watyrslacke between the land of the said Adam ... and the land of Robert Franckelayne’, Hemsworth. An undated thirteenth-century deed also has the term: ‘in a place called Briggeflat by le Water slacke’, Stubham.