Source : Webster's Revised Unabridged Dictionary (1913)

Compactness \Com*pact"ness\, n.
   The state or quality of being compact; close union of parts;
   density.

Source : WordNet®

compactness
     n 1: the spatial property of being crowded together [syn: {concentration},
           {density}, {denseness}] [ant: {distribution}]
     2: the consistency of a compact solid