Wordnet 3.0
NOUN (1)
1.
fish-like vertebrate with bony plates on head and upper body;
dominant in seas and rivers during the Devonian;
considered the earliest vertebrate with jaws;
The Collaborative International Dictionary of English v.0.48:
Placoderm \Plac"o*derm\, n. [Gr. pla`x, plako`s, tablet + de`rma
skin.] (Paleon.)
One of the Placodermi.
[1913 Webster]
WordNet (r) 3.0 (2006):
placoderm
n 1: fish-like vertebrate with bony plates on head and upper
body; dominant in seas and rivers during the Devonian;
considered the earliest vertebrate with jaws