\Plac"oid\, a. [Gr. ?, ?, a tablet + -oid.] (Zo["o]l.)
Platelike; having irregular, platelike, bony scales, often
bearing spines; pertaining to the placoids.

\Plac"oid\, n. (Zo["o]l.)
(a) Any fish having placoid scales, as the sharks.
(b) One of the Placoides.