The Collaborative International Dictionary of English v.0.48:

Homunculus \Ho*mun"cu*lus\, n.; pl. Homunculi. [L., dim. of
   homo man.]
   A little man; a dwarf; a manikin. --Sterne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

homunculus
    n 1: a person who is very small but who is not otherwise
         deformed or abnormal [syn: manikin, mannikin,
         homunculus]
    2: a tiny fully formed individual that (according to the
       discredited theory of preformation) is supposed to be present
       in the sperm cell