actinost

Century Dictionary and Cyclopedia

1. n. In ichthyology, one of the bones which in true fishes immediately support the rays of the pectoral and ventral fins. They are generally, in the pectorals, four in number, but sometimes, as in some pediculates, are reduced to two, and sometimes, as in ganoids, increased to more than four; they are rarely atrophied. Gill.

Wiktionary

1. n. A bone at the base of a paired fin (of a fish)

GNU Webster's 1913

1. n. One of the bones at the base of a paired fin of a fish.