Source : Webster's Revised Unabridged Dictionary (1913)

Acalephae \Ac`a*le"ph[ae]\, n. pl. [NL., from Gr. ?, a nettle.]
   A group of C[oe]lenterata, including the Medus[ae] or
   jellyfishes, and hydroids; -- so called from the stinging
   power they possess. Sometimes called {sea nettles}.