A small round pin used in certain locks to prevent any but the right key from operating the lock.(noun)
The Century Dictionary (Public Domain)
Use "pin-tumbler" in a sentence
"Although the imprint of the key in the lining of the wallet might not have been clear enough to make an accurate copy of the key, it did at least show that the key fitted a pin-tumbler lock with seven pins."
"Virtually all conventional pin-tumbler locks are vulnerable to this method of attack, and frankly nobody has really considered it or looked at it before."