Chockablock started out as a nautical term. A block is a metal or wooden case with one or more pulleys inside. Sometimes, two or more blocks are used as part of a rope and pulley system called a "block and tackle" to provide a mechanical advantage—as, for example, when hoisting a sail on a traditional sailing ship. When the rope is pulled as far as it will go, the blocks are tight together and are said to be chockablock. Non-nautical types associated the chock in chockablock with chock-full, which goes back to Middle English chokkefull, meaning "full to the limit" (a figurative use of "full to choking"). We thus gave chockablock the additional meaning "filled up." Chockablock can also be an adverb meaning "as close or as completely as possible," as in "families living chockablock" or the seemingly redundant "chockablock full."