c.1300, "lean, thin, emaciated" (of persons or animals), from O.Fr. megre, maigre, from L. macrum (nom. macer) "lean, thin," from PIE *makro- (see macro-). Of material things (land, food, etc.) from 1501.
I just thought it was interesting how this word was directly related to emaciated, but it seems that the two words diverged in their applications (things vs. people).