IPA: /ˈɒp.tɪ.mɪst/
KK: /ˈɑp.tɪ.mɪst/
A person who tends to see the positive side of things and expects good outcomes.
She is an optimist who always believes that everything will turn out well.
Optimist → It is formed from "optimus" (meaning best) and the suffix "-ist" (meaning one who practices or is concerned with). An optimist is one who believes in the best possible outcome or has a hopeful outlook on life.
Think of someone who believes in the 'best' ('optimus') outcomes — that's what an optimist does.