A small constellation north of Aquila; the Arrow. [1913 Webster]
The keystone of an arch. Gwilt. [1913 Webster]
The distance from a point in a curve to the chord; also, the versed sine of an arc; -- so called from its resemblance to an arrow resting on the bow and string. [1913 Webster]
The larger of the two otoliths, or ear bones, found in most fishes. [1913 Webster]
A genus of transparent, free-swimming marine worms having lateral and caudal fins, and capable of swimming rapidly. It is the type of the class Chætognatha. [1913 Webster]

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