Definition of "Pollyanna"

Pollyanna Pocket was small, with long floppy ears and a tail that coiled upwards in a little ringlet. She was a bouncy, happy young dog, who frolicked all day

2014, Dot and the Waves, page 10‎

I never wanna hear / From any cheerful Pollyannas / Who tell you Fate supplies a mate / It's all bananas

1930, George Gershwin, Ira Gershwin (lyrics and music), “But Not for Me”, performed by Ginger Rogers

‘Next time we’re going to have fun, OK?’ I wanted this album to go towards the light. You indulge in the grief to a certain point, but then you have to be a little bit Pollyanna.”

2017 November 12, Miranda Sawyer, “Björk: ‘People miss the jokes. A lot of it is me taking the piss out of myself’”, in The Guardian‎