Source : Webster's Revised Unabridged Dictionary (1913)

Au fond \Au` fond"\ [F., lit., at the bottom.]
   At bottom; fundamentally; essentially.

Source : WordNet®

au fond
     adv : at bottom or by one's (or its) very nature; "He is basically
           dishonest"; "the argument was essentially a technical
           one"; "for all his bluster he is in essence a shy
           person" [syn: {basically}, {fundamentally}, {essentially},
            {in essence}]