The Collaborative International Dictionary of English v.0.48:

Meddlesome \Med"dle*some\, a.
   Given to meddling; apt to interpose in the affairs of others;
   officiously intrusive. -- Med"dle*some*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

meddlesomeness
    n 1: aggressiveness as evidenced by intruding; by advancing
         yourself or your ideas without invitation [syn:
         intrusiveness, meddlesomeness, officiousness]