The Collaborative International Dictionary of English v.0.48:

Trembler \Trem"bler\, n.
   One who trembles.
   [1913 Webster]

   2. Any of certain West Indian birds of the genera
      Cinclocerthia and Rhamphocinclus, of the family
      Mimidae.
      [Webster 1913 Suppl.]

   3. (Elec.) The vibrating hammer, or spring contact piece of a
      hammer break, as of the electric ignition apparatus for an
      internal-combustion engine.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

trembler
    n 1: one who quakes and trembles with (or as with) fear [syn:
         quaker, trembler]