The Collaborative International Dictionary of English v.0.48:

Oaf \Oaf\ ([=o]f), n. [See Auf.]
   1. Originally, an elf's child; a changeling left by fairies
      or goblins; hence, a deformed or foolish child; a
      simpleton; an idiot.
      [1913 Webster]

   2. A clumsy or awkward person.

   Syn: klutz, clod, lummox, stumblebum.
        [PJC]

The Collaborative International Dictionary of English v.0.48:

Auf \Auf\ ([add]f), n. [OE. auph, aulf, fr. Icel. [=a]lfr elf.
   See Elf.] [Also spelt oaf, ouphe.]
   A changeling or elf child, -- that is, one left by fairies; a
   deformed or foolish child; a simpleton; an oaf. [Obs.]
   --Drayton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oaf
    n 1: an awkward stupid person [syn: lout, clod,
         stumblebum, goon, oaf, lubber, lummox, lump,
         gawk]