Definition of "key-piece" [key-piece]

• A log which, caught by a rock or other obstruction in a stream, causes a jam of logs. (noun)

The Century Dictionary (Public Domain)

• "The key-piece A is now put in position, and the puzzle is completed."
• "The "key-piece" of the jam was fully exposed, and once it was cut in two it would no longer hold the accumulation of logs together."
• "One log after another was detached from the disordered mass and sent whirling off down stream, until at the end of an hour's arduous exertion, the key-piece -- that is, the log that had caused all the trouble -- was found."