/os"treuh koh derrm'/ , n.
any of several extinct jawless fishes of the Ordovician, Silurian, and Devonian periods, having the body enclosed in an armor of bony plates.
[ 1890-95; Ostracodermi, pl. of Ostracodermus ostrakódermos with a shell, equiv. to óstrako ( n ) shell, tile + -dermos -DERM ]