pollyanna

/P AA0 L IY0 AE1 N AH0/
noun
  1. 1

    One who is persistently cheerful and optimistic, even when given cause not to be so.

    โ€œYou call her an optimist, but I call her an obnoxious Pollyanna.โ€

Source: https://en.wiktionary.org/wiki/Pollyanna, https://en.wiktionary.org/wiki/pollyanna