The Collaborative International Dictionary of English v.0.48:

Quidnunc \Quid"nunc\, n. [L., what now?]
   One who is curious to know everything that passes; one who
   knows, or pretends to know, all that is going on. "The idle
   stories of quidnuncs." --Motley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quidnunc
    n 1: a person who meddles in the affairs of others [syn:
         busybody, nosy-parker, nosey-parker, quidnunc]