The Collaborative International Dictionary of English v.0.48:

Lavender \Lav"en*der\, n. [OE. lavendre, F. lavande, It. lavanda
   lavender, a washing, fr. L. lavare to wash; cf. It.
   lsavendola, LL. lavendula. So called because it was used in
   bathing and washing. See Lave. to wash, and cf.
   Lavender.]
   1. (Bot.) An aromatic plant of the genus Lavandula
      (Lavandula vera), common in the south of Europe. It
      yields and oil used in medicine and perfumery. The Spike
      lavender (Lavandula Spica) yields a coarser oil (oil of
      spike), used in the arts.
      [1913 Webster]

   2. The pale, purplish color of lavender flowers, paler and
      more delicate than lilac.
      [1913 Webster]

   Lavender cotton (Bot.), a low, twiggy, aromatic shrub
      (Santolina Cham[ae]cyparissus) of the Mediterranean
      region, formerly used as a vermifuge, etc., and still used
      to keep moths from wardrobes. Also called ground
      cypress.

   Lavender water, a perfume, toilet water, or shaving lotion
      containing the essential oil of lavender, and sometimes
      the essential oil of bergamot, and essence of ambergris.


   Sea lavender. (Bot.) See Marsh rosemary.

   To lay in lavender.
      (a) To lay away, as clothing, with sprigs of lavender.
      (b) To pawn. [Obs.]
          [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Santolina chamaecyparissus
    n 1: branching aromatic Mediterranean shrub with woolly stems
         and leaves and yellow flowers [syn: lavender cotton,
         Santolina chamaecyparissus]