The whole thing.

I've seen it suggested that this phrase refers to all of a shopkeeper's possessions - the stock in trade, the items stored in barrels and the lock to the door. That's entirely fanciful though - the 'whole thing' in question when this phrase originated was a musket. Muskets were composed of three parts:

- The lock, or flintlock, which is the firing mechanism. Various forms of 'lock' muskets were used from the 1400s onwards, e.g. firelocks, flintlocks, matchlocks etc. The term 'lock' was probably adopted because the mechanism resembles a door lock.

- The stock, which is the wooden butt-end of the gun. 'Stock' is the old term for wooden butt or stump and is a generic term for a solid base. It was used as early as 1495 in association with Tudor guns, in a bill for 'gonne stokkes'. See also laughing stock.

- The barrel, i.e. a cylindrical object, is an even older word and was well-established by the 15th century. This is the least obvious of these three terms to have been chosen to name a musket part. After all, in the 15th century people would have been very familiar with barrels as the squat coopered tubs used for storage - hardly similar to the parallel-sided cylindrical tubes that were used in muskets. It may have been that the term migrated from cannons or other sorts of gun which were more barrel-shaped.

Given the antiquity of the three words that make up the phrase and the fact that guns have been in use since at least the Hundred Years' War in 1450, and even earlier in other countries e.g. China, we might expect it to be very old. In fact it isn't particularly; the earliest use of it appears to come from the letters of Sir Walter Scott in 1817:

"Like the High-landman's gun, she wants stock, lock, and barrel, to put her into repair."

Scott wasn't shy of inventing new phrases in his writing and it's highly likely that he coined 'stock, lock and barrel'. The reference to 'lock' coming at a time when the use of flintlocks was in decline might be thought as evidence against any link between them. Scott constantly referred back in time in his work though, as is fitting for the man who is credited with inventing the historical novel, and many of his books are set in the 15th and 16th centuries.

There are several citations of the phrase in that form from soon after Scott. It quickly crossed the Atlantic and in 1830 appeared in The Trenton Emporium newspaper:

"The country is ruined, stock, lock and barrel."

It isn't until 1842 though, in William Thompson's collection of humourous letters Major Jones' Courtship, that we see the phrase as we now use it:

"All moved, lock, stock, and barrel."

Rudyard Kipling came close to giving us a definition of the term in 1891, in Light That Failed:

"The whole thing, lock, stock, and barrel, isn't worth one big yellow sea-poppy."

Why and how the change from 'stock, lock and barrel' was made we don't know now. It's possible that 'lock, stock and barrel' just has a better ring to it.