A short spar, at the bows of a ship, that serves as a flagpole to fly a flag (a jack)(noun)
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Use "jackstaff" in a sentence
"The effect of each aberration is telling: The fiery, foreground plume draws our eyes to the Temeraire's ghostly, imagined masts, and to its broken spar that hangs limply at front, no longer supporting a jackstaff or the Union flag that was removed when it was sold to a ship-breaker."
"Would you bear me out in that, relatively speaking, with her jackstaff jerking at her pennyladders, why not, and sizing a fair sail, knowest thout the kind?"
"The Austran ensign drooped from the jackstaff in the heavy still air that blanketed the harbor."