It's a perfectly good English word - a nautical term, but one which is rapidly becoming obsolete. Let's put it into context.
Imagine a scene from a few centuries ago: a ship is in full sail on the high seas. At this point, you may care to dig out your CD of classic 1970s TV themes - The Onedin Line1 is ideal. Timbers audibly groan as the vessel pitches and rolls through the swell. A sudden squall blows up. On the storm-lashed decks, the crew strain at the ropes as the captain frantically tries to plot a narrow course between treacherous rocks, when disaster strikes! The ship is holed beneath the water line. It's all hands to the pumps to prevent the vessel from sinking. Assuming the crew get out of this alive, when the ship finally limps into port, they might need to repair the futtocks.
They're ship's timbers - crooked ones which are scarfed2 together to form part of the compound ribs of the vessel.
In fact the term is also used elsewhere on board. The eyes of the topmast rigging are secured to iron futtock plates, and futtock shrouds are ropes which attach a 'top' or mast platform to the mast beneath it.
Our larger ships may no longer be built from wood, yet smaller sailing dinghies are, of course. Boat geeks today will take a break from the many hours they spend varnishing, caulking and replacing the rotten wood of their vessels, and, sitting around with a cup of tea, will still discuss the merits of futtocks, scarf joints and other arcane nautical jargon.
The word probably derives from 'foot hook' - the foot of curved, or hooked timbers. Over the centuries the pronunciation will have contracted to futtock, just as boatswain has become bosun and forecastle fo'c'sle. In the same way, fans of the well known Two Ronnies 'Four Candles' sketch may remember the closing scene as Ronnie Corbett misunderstands a similar contraction for 'bill hooks'.
And it is with the other Ronnie that we end. Futtocks End was the first of three 'silent' comedy films written by and starring the late Ronnie Barker. Released in 1970, it features Barker as General Futtock, who engages in a series of saucy goings-on with a set of somewhat dysfunctional house guests at his stately home. Other stars included Michael Hordern as the Butler, and Richard O'Sullivan as the Boots. Ronnie Corbett was to co-star in the next two instalments, The Picnic in 1975, and By The Sea in 1982.