The Collaborative International Dictionary of English v.0.48:

Meddler \Med"dler\, n.
   One who meddles; one who interferes or busies himself with
   things in which he has no concern; an officious person; a
   busybody.
   [1913 Webster]

WordNet (r) 3.0 (2006):

meddler
    n 1: an officious annoying person who interferes with others

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "meddler":
   Dutch uncle, Paul Pry, Polonius, admonisher, adviser,
   backseat driver, busybody, butt-in, buttinsky, confidant,
   consultant, counsel, counselor, expert, guide, instructor,
   intermeddler, kibitzer, mentor, monitor, nestor, orienter,
   pragmatist, preceptist, prier, pry, quidnunc, rubberneck, snoop,
   snooper, teacher, yenta