【Annotate】 , 【gloss】 and their corresponding nouns annotation, 【gloss】 mean, as verbs, to add or append comment, or as nouns, an added or appended comment intended to be helpful in interpreting a passage or text.

One annotates a text (as of a literary work) when one furnishes it with critical, historical, or explanatory notes (as footnotes, marginal notes, or notes in an appendix)

• 【annotate】 the works of Milton
• an annotated edition of Shakespeare′s sonnets

The subject of an annotation may be any word, passage, or detail which is capable of being explained to the advantage of the reader or student. One glosses a word or phrase which is obscure in meaning because foreign, obsolete, rare, or technical by providing its definition (as in a marginal or interlinear note) or one glosses a text when one supplies definitions of its difficult words and phrases.

• medieval scholars, when they found in a Latin text a word not familiar to them, were accustomed to 【gloss】 it
  —Krutchy

The word sometimes conveys (possibly by confusion with 【gloss】 , to give a luster to) a derogatory implication of perversion or sophistication of meaning or fact.

• trying to 【gloss】 away the irrationalities of the universe
  —Edmany