The Collaborative International Dictionary of English v.0.48:

Tamarisk \Tam"a*risk\, n. [L. tamariscus, also tamarix,
   tamarice, Skr. tam[=a]la, tam[=a]laka, a tree with a very
   dark bark; cf. tamas darkness: cf. F. tamarisc, tamarix,
   tamaris.] (Bot.)
   Any shrub or tree of the genus Tamarix, the species of
   which are European and Asiatic. They have minute scalelike
   leaves, and small flowers in spikes. An Arabian species
   (Tamarix mannifera) is the source of one kind of manna.
   [1913 Webster]

   Tamarisk salt tree, an East Indian tree (Tamarix
      orientalis) which produces an incrustation of salt.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tamarisk
    n 1: any shrub or small tree of the genus Tamarix having small
         scalelike or needle-shaped leaves and feathery racemes of
         small white or pinkish flowers; of mostly coastal areas
         with saline soil

Easton's 1897 Bible Dictionary:

Tamarisk
   Heb. 'eshel (Gen. 21:33; 1 Sam. 22:6; 31:13, in the R.V.; but in
   A.V., "grove," "tree"); Arab. asal. Seven species of this tree
   are found in Palestine. It is a "very graceful tree, with long
   feathery branches and tufts closely clad with the minutest of
   leaves, and surmounted in spring with spikes of beautiful pink
   blosoms, which seem to envelop the whole tree in one gauzy sheet
   of colour" (Tristram's Nat. Hist.).