What does "arris" mean?

Arris: The sharp edge or salient angle formed by two surfaces meeting each other, whether plane or curved; -- applied particularly to the edges in moldings, and to the raised edges which separate the flutings in a Doric column. P. Cyc. Arris fillet, a triangular piece of wood used to raise the slates of a roof against a chimney or wall, to throw off the rain. Gwilt. -- Arris gutter, a gutter of a V form fixed to the eaves of a building. Gwilt.