DIARY, n. A daily record of that part of one’s life, which he can relate to himself without blushing.

Ambrose Bierce (1842-1914?) American writer and journalist

“Diary,” The Cynic’s Word Book (1906)
    (Source)

Included in The Devil's Dictionary (1911). Originally published in the "Devil's Dictionary" column in the San Francisco Wasp (1882-05-24).