Is it acceptable to cite a textbook for basic background in a master's thesis? There's one theoretical concept I feel I need to explain briefly in the literature review portion of my MA thesis, but it's very slightly tangential and I don't want to spend more than a paragraph on it. A textbook provides the most all-encompassing, thumbnail sketch of this concept, which would allow me to explain it while citing a single source rather than three or four journal articles. 

Would it be déclassé to use a textbook as a reference in a MA thesis for this purpose?
You are right that listing a textbook is generally not seen as 'academic' enough. But I think it would make sense to cite it in a literature review with a note like, 'For a good basic overview of this subject, see…'. This I think is acceptable, given that the rest of your thesis shows awareness of more technical pieces as well.