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

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "timer":
   Big Ben, annalist, automatic switch, calendar maker, calendarist,
   channel selector, check valve, chronicler, chronographer,
   chronologer, chronologist, chronometer, clock, clock movement,
   clockmaker, clockworks, contour follower, control valve, diarist,
   electronic control, emergency control, finder switch, flowmanostat,
   horologe, horologist, horologium, internal selector, rectifier,
   register regulator, safety control, safety fuse, safety stop,
   safety switch, safety valve, selector switch, sequence switch,
   servo valve, thermoswitch, ticker, timekeeper, timepiece, turnip,
   voltage regulator, voltage stabilizer, watch, watchmaker,
   watchworks