A size of printing paper, or in British universities, a size of paper used for academic work, or a type of student at certain colleges.
From French demi meaning 'half,' from Latin dimidius. The paper size is so called because it's half the size of a larger standard sheet.
At Oxford University, being a 'demy' of Magdalen College is actually a prestigious scholarship—the word has changed meaning from just being about paper size to representing academic achievement!
Complete word intelligence in one call. Free tier — 50 lookups/day.