Source : Webster's Revised Unabridged Dictionary (1913)

Diary \Di"a*ry\, n.; pl. {Diaries}. [L. diarium, fr. dies day.
   See {Deity}.]
   A register of daily events or transactions; a daily record; a
   journal; a blank book dated for the record of daily
   memoranda; as, a diary of the weather; a physician's diary.

Diary \Di"a*ry\, a.
   lasting for one day; as, a diary fever. [Obs.] ``Diary
   ague.'' --Bacon.

Source : WordNet®

diary
     n 1: a daily written record of (usually personal) experiences and
          observations [syn: {journal}]
     2: a personal journal (as a physical object)