Английский Этимологический словарь - gloss (2)

- "explanation," 1548, gloze, from L. glossa "obsolete or foreign word," from Gk. glossa (Ionic), glotta (Attic) "obscure word, language," lit. "tongue." Extended sense of "explain away" is 1638, from idea of a note inserted in the margin of a text to explain a difficult word.