From Longman Business Dictionary
optimistop·ti·mist /ˈɒptəmɪstˈɑːp-/ noun [countableC] someone who believes things will get better or be more successful in the futureAs major companies in this sector continue to show poor results, even optimists are getting worried.
→ compare pessimist —optimistic adjectiveadjHe remains optimistic about the company’s long-term prospects.
The government’sover-optimistic economic forecasts have encouraged manufacturers to put too many products into their inventories.