The Collaborative International Dictionary of English v.0.48:

Nanism \Na"nism\ (n[=a]"n[i^]z'm; n[a^]n"[i^]z'm), n. [Gr.
   na^nos + -ism: cf. F. nanisme.]
   The condition of being abnormally small in stature; dwarfism;
   dwarfishness; -- opposed to gigantism.
   [Webster 1913 Suppl.] Nanjing

WordNet (r) 3.0 (2006):

nanism
    n 1: a genetic abnormality resulting in short stature [syn:
         dwarfism, nanism]