Source : Webster's Revised Unabridged Dictionary (1913)

Cnida \Cni"da\, n.; pl. {Cnid[ae]}. [NL., fr. Gr. ? nettle, sea
   nettle.] (Zo["o]l.)
   One of the peculiar stinging, cells found in C[oe]lenterata;
   a nematocyst; a lasso cell.