IPA: /ˈdaɪərɪst/
KK: /ˈdaɪərist/
A person who regularly writes in a diary to record their thoughts, experiences, and feelings.
As a diarist, she documented her travels and personal reflections every day.
Diarist → It is formed from "diary" (from Latin *diarium*, meaning daily allowance or journal) and "-ist" (meaning a person who practices or is concerned with something). A diarist is a person who keeps a diary or journal, documenting daily events or thoughts.
Think of a 'diary' as a place where daily thoughts are recorded, and the '-ist' means a person who does that. So, a diarist is someone who writes in a diary.