Affording no holds; having a smooth unbroken surface.

a thick wind-crust, of a kind liable to slip and create an avalanche; cf. slab avalanche n. at slab, n.1 compounds 3.

In a high degree or measure; to a great extent; exceedingly, extremely, greatly. Mountaineering. very difficult, very severe: two of the categories…

Mountaineering. Of or pertaining to a rock face on which good climbing holds are hard to find.

Of rock, a rock face, etc.: friable, crumbly, loose; consisting of such rock, esp. characterized as unsafe or unpleasant to climb.