The Collaborative International Dictionary of English v.0.48:

Actuary \Ac"tu*a*ry\, n.; pl. Actuaries. [L. actuarius
   copyist, clerk, fr. actus, p. p. of agere to do, act.]
   1. (Law) A registrar or clerk; -- used originally in courts
      of civil law jurisdiction, but in Europe used for a clerk
      or registrar generally.
      [1913 Webster]

   2. The computing official of an insurance company; one whose
      profession it is to calculate for insurance companies the
      risks and premiums for life, fire, and other insurances.
      [1913 Webster]

WordNet (r) 3.0 (2006):

actuary
    n 1: someone versed in the collection and interpretation of
         numerical data (especially someone who uses statistics to
         calculate insurance premiums) [syn: statistician,
         actuary]