Definition from Wiktionary, the free dictionary
- (nautical) that part of an anchor cable which is abaft the bitts and thus remains inboard when a ship is riding at anchor
- Note: To pay out a rope to the bitter end means to pay it all out
- (idiomatic) The end of a long and difficult process.
- (nautical) the final six fathoms of anchor chain before the point of attachment in the chain locker of modern U.S.naval vessels, with these six fathoms often painted blue, white and red to warn deck hands of the end of available anchor chain.
Usage notes 
Related terms 
the end of a long and difficult process