The Collaborative International Dictionary of English v.0.48:

Diary \Di"a*ry\ (d[imac]"[.a]*r[y^]), 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.
   [1913 Webster]