The Collaborative International Dictionary of English v.0.48:

Annotate \An"no*tate\, v. t. [imp. & p. p. Annotated; p. pr. &
   vb. n. Annotating.] [L. annotatus; p. p. of annotare to
   annotate; ad + notare to mark, nota mark. See Note, n.]
   To explain or criticize by notes; as, to annotate the works
   of Bacon.
   [1913 Webster]