placodermPronunciation: /ˈplakə(ʊ)dəːm/Definition of placoderm noun a fossil fish of the Devonian period, having the front part of the body encased in broad flat bony plates. Class Placodermi: several orders Origin: mid 19th century: from Greek plax, plak- 'flat plate' + derma 'skin'placoderm in other Oxford dictionaries Definition of placoderm in the US English dictionary
