Source : Webster's Revised Unabridged Dictionary (1913)

Meddlesome \Med"dle*some\, a.
   Given to meddling; apt to interpose in the affairs of others;
   officiously intrusive. -- {Med"dle*some*ness}, n.

Source : WordNet®

meddlesomeness
     n : aggressiveness as evidenced by intruding; by advancing
         yourself or your ideas without invitation [syn: {intrusiveness},
          {officiousness}]