The Collaborative International Dictionary of English v.0.48:

Timer \Tim"er\, n.
   1. A timekeeper; especially, a watch by which small intervals
      of time can be measured; a kind of stop watch. It is used
      for timing the speed of horses, machinery, etc.
      [1913 Webster]

   2. (Internal-combustion Engines) In electric ignition, an
      adjustable device for automatically timing the spark.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

timer
    n 1: a timepiece that measures a time interval and signals its
         end
    2: (sports) an official who keeps track of the time elapsed
       [syn: timekeeper, timer]
    3: a regulator that activates or deactivates a mechanism at set
       times