Relating to or characteristic of a diary or daily record of events and personal thoughts.
From Latin 'diarium' (daily allowance, day book) + English suffix '-al' (relating to), evolving from 'dies' (day).
The word 'diary' comes from the same Latin root meaning 'daily'—that's why it's diarial and not 'diaryish'! English loves Latin suffixes for turning nouns into adjectives.
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