Webster’s Revised Unabridged Dictionary · 1913
Placoid
Plac′oid (plăk′oid), a. [Gr. πλάξ, πλακός, a tablet + -oid.] (Zoöl.) Platelike; having irregular, platelike, bony scales, often bearing spines; pertaining to the placoids.
Plac′oid, n. (Zoöl.) (a) Any fish having placoid scales, as the sharks. (b) One of the Placoides.