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]

The Collaborative International Dictionary of English v.0.48:

Annotate \An"no*tate\, v. i.
   To make notes or comments; -- with on or upon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

annotate
    v 1: add explanatory notes to or supply with critical comments;
         "The scholar annotated the early edition of a famous novel"
         [syn: annotate, footnote]
    2: provide interlinear explanations for words or phrases; "He
       annotated on what his teacher had written" [syn: gloss,
       comment, annotate]

The Free On-line Dictionary of Computing (30 December 2018):

annotation
annotate

   1.  Extra information associated with a
   particular point in a document or program.  Annotations may be
   added either by a compiler or by the programmer.  They are
   not usually essential to the correct function of the program
   but give hints to improve performance.

   2.  A new commentary node linked to an existing
   node.  If readers, as well as authors, can annotate nodes,
   then they can immediately provide feedback if the information
   is misleading, out of date or plain wrong.

   (1995-11-26)