This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. A short spar, at the bows of a ship, that serves as a flagpole to fly a flag (a jack)

"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."

land breeze    agley    jackstay    beriberi    épée    jib boom    zeolite    at-sea    whinstone    gunnel