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]