Breadcrumb Home > Dictionary > Index P placoderm: Meaning and Definition of Find definitions for: plac•o•derm Pronunciation: (plak'u-dûrm"), [key] — n. any of various extinct jawed fishes of the class Placodermi, dominant in seas and rivers during the Devonian Period and characterized by bony armored plates on the head and upper trunk. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: placoderm (Thesaurus) placode placoid ✖ Related Content Daily Word Quiz: tendentious Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language