horology

from WordNet (r) 3.0 (2006)

horology
    n 1: the art of designing and making clocks

from The Collaborative International Dictionary of English v.0.48

Horology \Ho*rol"o*gy\, n. [See {Horologe}.]
   The science of measuring time, or the principles and art of
   constructing instruments for measuring and indicating
   portions of time, as clocks, watches, dials, etc.
   [1913 Webster]