The Collaborative International Dictionary of English v.0.48:

Tick \Tick\, n. [OE. tike, teke; akin to D. teek, G. zecke. Cf.
   Tike a tick.] (Zool.)
      (a) Any one of numerous species of large parasitic mites
          which attach themselves to, and suck the blood of,
          cattle, dogs, and many other animals. When filled with
          blood they become ovate, much swollen, and usually
          livid red in color. Some of the species often attach
          themselves to the human body. The young are active and
          have at first but six legs.
      (b) Any one of several species of dipterous insects having
          a flattened and usually wingless body, as the bird
          ticks (see under Bird) and sheep tick (see under
          Sheep).
          [1913 Webster]

   Tick bean, a small bean used for feeding horses and other
      animals.

   Tick trefoil (Bot.), a name given to many plants of the
      leguminous genus Desmodium, which have trifoliate
      leaves, and joined pods roughened with minute hooked hairs
      by which the joints adhere to clothing and to the fleece
      of sheep.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tick trefoil
    n 1: any of various tropical and subtropical plants having
         trifoliate leaves and rough sticky pod sections or loments
         [syn: tick trefoil, beggar lice, beggar's lice]