The Collaborative International Dictionary of English v.0.48:

Timekeeper \Time"keep`er\ (t[imac]m"k[=e]p`[~e]r), n.
   1. A clock, watch, or other chronometer; a timepiece.
      [1913 Webster]

   2. A person who keeps, marks, regulates, or determines the
      time. Specifically:
      [1913 Webster]
      (a) A person who keeps a record of the time spent by
          workmen at their work.
          [1913 Webster]
      (b) One who gives the time for the departure of
          conveyances.
          [1913 Webster]
      (c) One who marks the time in musical performances.
          [1913 Webster]
      (d) One appointed to mark and declare the time of
          participants in races or other contests.
          [1913 Webster]

WordNet (r) 3.0 (2006):

timekeeper
    n 1: (sports) an official who keeps track of the time elapsed
         [syn: timekeeper, timer]
    2: a clerk who keeps track of the hours worked by employees
    3: a measuring instrument or device for keeping time [syn:
       timepiece, timekeeper, horologe]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "timekeeper":
   Big Ben, accountant, amanuensis, annalist, archivist, bookkeeper,
   calendar maker, calendarist, chronicler, chronographer,
   chronologer, chronologist, chronometer, clerk, clock,
   clock movement, clockmaker, clockworks, diarist, documentalist,
   engraver, filing clerk, horologe, horologist, horologium,
   librarian, marker, notary, notary public, prothonotary,
   record clerk, recorder, recordist, register, registrar,
   scorekeeper, scorer, scribe, scrivener, secretary, stenographer,
   stonecutter, ticker, timepiece, timer, turnip, watch, watchmaker,
   watchworks