Pol ‧ ly ‧ an ‧ na /ˌpɒliˈænə $ ˌpɑː-/ BrE AmE noun [countable usually singular]
[ Date: 1900-2000 ; Origin: Pollyanna , main character in the book Pollyanna (1913) by Eleanor Porter ]
someone who is always happy and always thinks something good is going to happen