<embryology> Area of thickened ectoderm in the embryo from which a nerve ganglion or a sense organ will develop. ... (31 Dec 1997) ... 
(plak´ōd) a platelike structure, especially a thickening of the ectoderm marking the site of future development in the early embryo of an organ of special sense; for example the otic placode is for the ear, the lens placode is for the eye, and the nasal placode is for the nose.
Area of thickened ectoderm in the embryo from which a nerve ganglion, or a sense organ will develop.
Type: Term Pronunciation: plak′ōd Definitions: 1. Local thickening in the embryonic ectodermal layer; the cells of the placode ordinarily constitute a primordial group from which a sense organ or ganglion develops.
Greek plax = plate or flat, and eidos = shape or form.