Source : Webster's Revised Unabridged Dictionary (1913)

Diminutiveness \Di*min"u*tive*ness\, n.
   The quality of being diminutive; smallness; littleness;
   minuteness.

Source : WordNet®

diminutiveness
     n : the property of being very small in size [syn: {minuteness},
          {petiteness}, {tininess}, {weeness}]