Description:

The modifier 'ruk' refers to the quality of flatness, and at the same time thinness, which can lead to a degree of ambiguity.

Modifier:

As a modifier, ruk can refer to something having a flat geometry, i.e., lack of curvature, or to bring thin and sheet-like, which can then involve random curvature. To imply true geometric flatness you could say 'zrano ruk'.

Noun:

As a noun, 'ruk' means a flat it sheet-like object, like a sheet or tarp (although an actual bedsheet would probably be referred to as 'mawa', 'cover').

Verb:

As a verb, 'ruk' is a transitive skurun verb meaning to flatten or  into a sheet.