Source : Webster's Revised Unabridged Dictionary (1913)

Annotto \An*not"to\, Arnotto \Ar*not"to\, n. [Perh. the native
   name.]
   A red or yellowish-red dyeing material, prepared from the
   pulp surrounding the seeds of a tree ({Bixa orellana})
   belonging to the tropical regions of America. It is used for
   coloring cheese, butter, etc. [Written also {Anatto},
   {Anatta}, {Annatto}, {Annotta}, etc.]

Arnotto \Ar*not"to\, n.
   Same as {Annotto}.