IPA: /aɪˈdɪə.lɪs.tɪ.kli/
KK: /aɪˈdiːəˌlɪstɪkli/
In a way that is based on ideals or principles rather than practical considerations.
She approached the project idealistically, believing that everyone would work together for the common good.
Idealistically → It is formed from "ideal" (from Greek "idealis", meaning existing as a mental image or concept) and the suffix "-istically" (meaning in a manner relating to). The word "idealistically" refers to acting in a way that is guided by ideals or principles rather than practical considerations.
Think of someone acting according to their 'ideal' or perfect vision ('ideal') and doing so 'in a manner' ('-istically') that reflects those beliefs.