The sharp edge or ridge formed where two surfaces meet.
Arris is the sharp edge or ridge created where two surfaces meet at an angle. In stone carving and architectural work, preserving an arris means maintaining the clarity of that meeting line rather than unintentionally rounding it during refining, sanding, or polishing.
The term is useful when discussing the precision of edges, transitions between planes, and the quality of finish in carved stone.
Italian equivalent: spigolo. A deliberately sharp, unrounded edge may be described in Italian as spigolo vivo.
Etymology
English from Middle/Old French areste, 'beard of grain; sharp ridge,' related to modern French arête; ultimately from Latin arista, 'awn or beard of grain; fishbone.' The architectural sense is recorded in English from the 17th century.
Sculptor Notes
In marble carving, the arris is especially important during finishing. Abrasives can soften or round an edge unintentionally. A clean arris helps preserve the intended relationship between adjacent planes and contributes to the exceptionally crisp finish often seen in high-level Italian stonework. Cross-reference: Spigolo; Spigolo vivo.
References
https://www.collinsdictionary.com/dictionary/english/arris | https://www.dictionary.com/browse/arris