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a. The horizontally projecting edge of a stair tread.
b. A shield covering this edge.
2. A projecting edge of a molding.
1. (Building) the edge of a step or stair tread that projects beyond the riser
2. (Architecture) a projecting edge of a moulding, esp one that is half-round
[C18: from nose + -ing1]
a projecting edge, as the part of the tread of a step extending beyond the riser.