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 metal coupling device consisting of an oblong piece internally threaded at both ends into which the corresponding sections of two threaded rods are screwed in order to form a unit that can be adjusted for tension or length.

n. A coupling device consisting of two eyelets or other connection points connected in screw threads. The joint in between can be turned to shorten or lengthen the device with mechanical advantage provided by the screw threads.

n. A link threaded on both ends of a short bar which is used to pull objects together. (FM 55-501)

"The other end of each shroud and backstay is attached to an adjustable device called a turnbuckle."

coupling    coupler   

pipe-turnbuckle    single-screw turnbuckle   

diopter    derichment    plaser    paracompass    start/acceleration