EM

Em (noun) — a quad with a square body. 2. (noun) a linear unit (1/6 inch) used in printing.

“since `em quad' is hard to distinguish from `en quad', printers sometimes called it a `mutton quad'”

Em is a valid 2-letter word worth 4 points in Scrabble (and Words With Friends letter values vary). Below are its anagrams and the shorter words hidden inside it.