Lasting for one day: as, a diary fever.n. [= Sp. Pg. It. diario, ⟨ L. diarium, a daily allowance for soldiers, LL. also a diary, neut. of *diarius, adj., ⟨ dies, day: see dial, deity. The synonym journal is of the same ult. origin.]n. An account of daily events or transactions; a journal; specifically, a daily record kept by a person of any or all matters within his experience or observation: as, a diary of the weather; a traveler's diary.n. A book prepared for keeping a diary; especially, a book with blank leaves bearing printed dates for a daily record, often including other printed matter of current use or interest: as, a lawyers' diary.