Other forms: diaries
A diary is a book you write the day's events in. Keep a diary, in my diary, a diary entry.
In Britain it is also the appointments book, so putting something in the diary means booking it, which confuses Americans who say calendar. The Latin behind it is a daily allowance, and journal comes from the same idea by another road.
1noundiaryA book you write the day's events in.
“She wrote about her first day at school in her diary.”
diary is a book.
Latin diarium means a daily allowance, from dies, a day; journal comes from the same idea through French.
Proto-Indo-European
*dyew-
English, today
diary
Built from
From Latin diārium (“a daily allowance for soldiers, in Latin - also ‘diary’”), neuter of diārius, from diēs (“a day”) (whence also journal). Cognate with Spanish diario (“daily; diary”).
Etymology from Wiktionary, CC BY-SA