Source : Webster's Revised Unabridged Dictionary (1913)

Echinus \E*chi"nus\, n.; pl. {Echini}. [L., a hedgehog, sea
   urchin, Gr. ?.]
   1. (Zo["o]l.) A hedgehog.

   2. (Zo["o]l.) A genus of echinoderms, including the common
      edible sea urchin of Europe.

   3. (Arch.)
      (a) The rounded molding forming the bell of the capital of
          the Grecian Doric style, which is of a peculiar
          elastic curve. See {Entablature}.
      (b) The quarter-round molding (ovolo) of the Roman Doric
          style. See Illust. of {Column}
      (c) A name sometimes given to the egg and anchor or egg
          and dart molding, because that ornament is often
          identified with Roman Doric capital. The name probably
          alludes to the shape of the shell of the sea urchin.

Source : WordNet®

echinus
     n : ovolo molding between the shaft and the abacus of a Doric
         column
     [also: {echini} (pl)]