The Collaborative International Dictionary of English v.0.48:
Placodermi \Plac`o*der"mi\, n. pl. [NL., fr. Gr. pla`x, plako`s, a tablet + de`rma skin.] (Paleon.) An extinct group of fishes, supposed to be ganoids. The body and head were covered with large bony plates. See Illust. under Pterichthys, and Coccosteus. [1913 Webster]WordNet (r) 3.0 (2006):
Placodermi n 1: extinct group of bony-plated fishes with primitive jaws [syn: Placodermi, class Placodermi]