Slabbiness

1678, John Bunyan, The Pilgrim’s Progress, London: Nath. Ponder, Facsimile reproduction, London: Elliot Stock, 1875, Part 2, p. 183, The Way also was here very wearysom thorow Dirt and Slabbiness.

Source: wiktionary

[…] we took our courage in both hands and started at the first break in the downpour. The valley was choked with mist, and the road in a state of unutterable slabbiness: yet our enterprise was soon rewarded, for the weather had done its worst in the darkness, and the sunshine brought the vapours steaming up out of the meadows and banished them with the clouds across the summits of the hills.

Source: wiktionary

1895, W. P. Haskett Smith, “Wales” in Climbing in the British Isles, London: Longmans, Green, and Co., “The Arans,” Looking up from the lake the crag, which is a high dependence of Aran Benllyn, shows on the right an almost unrelieved slabbiness at an easy angle, which gives good practice in small footholds.

Source: wiktionary