SETA'CEOUS, adjective [Latin seta, a bristle.]

1. Bristly; set with strong hairs; consisting of strong hairs; as a stiff setaceous tail.

2. In botany, bristle-shaped; having the thickness and length of a bristle; as a setaceous seaf or leaflet.

Setaceous worm, a name given to a water worm that resembles a horse hair, vulgarly supposed to be an animated hair. But this is a mistake.