Source : Webster's Revised Unabridged Dictionary (1913)

Oaf \Oaf\ ([=o]f), n. [See {Auf}.]
   Originally, an elf's child; a changeling left by fairies or
   goblins; hence, a deformed or foolish child; a simpleton; an
   idiot.

Source : WordNet®

oaf
     n : an awkward stupid person [syn: {lout}, {clod}, {stumblebum},
          {goon}, {lubber}, {lummox}, {lump}, {gawk}]