Source : Webster's Revised Unabridged Dictionary (1913)

Thyrsus \Thyr"sus\, n.; pl. {Thyrsi}. [L., fr. Gr. ?. Cf.
   {Torso}.]
   1. A staff entwined with ivy, and surmounted by a pine cone,
      or by a bunch of vine or ivy leaves with grapes or
      berries. It is an attribute of Bacchus, and of the satyrs
      and others engaging in Bacchic rites.

            A good to grow on graves As twist about a thyrsus.
                                                  --Mrs.
                                                  Browning.

            In my hand I bear The thyrsus, tipped with fragrant
            cones of pine.                        --Longfellow.

   2. (Bot.) A species of inflorescence; a dense panicle, as in
      the lilac and horse-chestnut.

Source : WordNet®

thyrsus
     n : a dense flower cluster (as of the lilac or horse chestnut)
         in which the main axis is racemose and the branches are
         cymose [syn: {thyrse}]
     [also: {thyrsi} (pl)]