oversanguine

adjective

over·​san·​guine ˌō-vər-ˈsaŋ-gwən 

: too confident or optimistic : excessively sanguine

wasn't oversanguine about their prospects for success

"Fiscal experts" may not be infallible, but it is hard to believe that oversanguine revenue projections can be solely responsible for so pathetic a performance.

—James Gill

Word History

First Known Use

1710, in the meaning defined above