Sagitta

In geometry - the radial distance from the center of a chord of a circle to the closer curve - aka the radius minus the apothem. Presumably it looks like an arrow on a bow.

In astronomy - the above for a spherical mirror. Also, a constellation, the arrow.

Arrowworms - genus Sagitta.

Our boat on our Galapagos tour. Not exactly swift as an arrow, but definitely more comfy.