To furnish (a literary work) with critical commentary or explanatory notes; gloss.(verb-transitive)
To gloss a text.(verb-intransitive)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "annotate" in a sentence
"We all know that annotation requires such rigor of selection that one might say that to annotate is to omit."
"You can take the very best teachers and kind of annotate it, have it so everyone sees who is the very best at teaching this stuff."
"Gilbert and Quinn have whipped up a sweet little Blosxom plug-in for annotating blog entry: if you have a link that you think should be added to a Blosxom post, you click the "annotate" link, select the word from the post that you want to footnote, enter the link, and click submit -- voila, annotated post."