“Chock-a-block” means crammed so tightly together that nothing can move. Similar words are “chock-full” and “jam-packed.”
The derivation of the first part of the word, “chock,” isn’t clear but may have come from “chock-full,” or “choke-full,” meaning “full to choking.” This dates back to the 1400s and is found in Morte Arthur, circa 1400. It might also come from the verb “chokken,” as in the Middle English phrase “chokken togeder,” crammed together.
Later on, “chock” was used to mean the wedges of wood which are used to secure moving objects. These chocks were used on ships and are referred to in William Falconer’s, An universal dictionary of the marine, 1769: “Chock, a sort of wedge used to confine a cask or other weighty body, when the ship is in motion.”
A block and tackle is a pulley system used on sailing ships to hoist the sails. However, “chock-a-block” is not the result of wedging a block fixed with a chock. The phrase describes what occurs when the sail is raised to its fullest extent — when there is no more rope free and the blocks jam tightly together.
Frederick Chamier’s novel The Life of a Sailor, 1832 includes this figurative use of the term: “Here my lads is another messmate…” — “What, another!” roared a ruddy-faced midshipman of about eighteen. “He must stow himself away, for we are chock-a-block here.”
The earliest example in print appears to be in Richard H. Dana Jr’s Two years before the mast, 1840: “Hauling the reef-tackles chock-a-block.”
“Chock-a-block” also spawned an abbreviated version in the 1900s — chocka (or chocker). This arose from WWII UK military slang and meant “fed-up or disgruntled.” This was listed in Hunt and Pringles’ Service Slang, 1943: “Chocker, this is the sailor’s way of saying he is fed up or browned off.”
Chock-A-Block is also a BBC children’s television programme. “Chock-A-Block” was an extremely large yellow computer, modelled to resemble a mainframe of the time; it filled the entire studio and provided the entire backdrop for the show.
One last quote, from Somerset Maugham, 1946: “The city’s two or three inns were chock-a-block and men were sleeping three, four and five in a bed.”
Now that is chock-a-block!