Source : Webster's Revised Unabridged Dictionary (1913)

Gillyflower \Gil"ly*flow`er\, n. [OE. gilofre, gilofer, clove,
   OF. girofre, girofle, F. girofle: cf. F. girofl['e]e
   gillyflower, fr. girofle, Gr. ? clove tree; ? nut + ? leaf,
   akin to E. foliage. Cf. {Caryophyllus}, {July-flower}.]
   (Bot.)
   1. A name given by old writers to the clove pink ({Dianthus
      Caryophyllus}) but now to the common stock ({Matthiola
      incana}), a cruciferous plant with showy and fragrant
      blossoms, usually purplish, but often pink or white.

   2. A kind of apple, of a roundish conical shape, purplish red
      color, and having a large core. [Written also
      {gilliflower}.]

   {Clove gillflower}, the clove pink.

   {Marsh gillyflower}, the ragged robin ({Lychnis
      Flos-cuculi}).

   {Queen's, or Winter}, {gillyflower}, damewort.

   {Sea gillyflower}, the thrift ({Armeria vulgaris}).

   {Wall gillyflower}, the wallflower ({Cheiranthus Cheiri}).

   {Water gillyflower}, the water violet.

Source : WordNet®

water gillyflower
     n : a featherfoil of the eastern United States with submerged
         spongy inflated flower stalks and white flowers [syn: {American
         featherfoil}, {Hottonia inflata}]