The Collaborative International Dictionary of English v.0.48:

Gossiper \Gos"sip*er\, n.
   One given to gossip. --Beaconsfield.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gossiper
    n 1: a person given to gossiping and divulging personal
         information about others [syn: gossip, gossiper,
         gossipmonger, rumormonger, rumourmonger,
         newsmonger]