The Collaborative International Dictionary
Truss \Truss\, n. [OE. trusse, F. trousse, OF. also tourse; perhaps fr. L. tryrsus stalk, stem. Cf. Thyrsus, Torso, Trousers, Trousseau.]
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A bundle; a package; as, a truss of grass.
--Fabyan.Bearing a truss of trifles at his back.
--Spenser.Note: A truss of hay in England is 56 lbs. of old and 60 lbs. of new hay; a truss of straw is 36 lbs.
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A padded jacket or dress worn under armor, to protect the body from the effects of friction; also, a part of a woman's dress; a stomacher. [Obs.]
--Nares.Puts off his palmer's weed unto his truss, which bore The stains of ancient arms.
--Drayton. (Surg.) A bandage or apparatus used in cases of hernia, to keep up the reduced parts and hinder further protrusion, and for other purposes.
(Bot.) A tuft of flowers formed at the top of the main stalk, or stem, of certain plants.
(Naut.) The rope or iron used to keep the center of a yard to the mast.
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(Arch. & Engin.) An assemblage of members of wood or metal, supported at two points, and arranged to transmit pressure vertically to those points, with the least possible strain across the length of any member. Architectural trusses when left visible, as in open timber roofs, often contain members not needed for construction, or are built with greater massiveness than is requisite, or are composed in unscientific ways in accordance with the exigencies of style.
Truss rod, a rod which forms the tension member of a trussed beam, or a tie rod in a truss.
Wikipedia
The truss rod is part of a guitar or other fretted, stringed-instruments that stabilizes the lengthwise forward curvature (also called relief), of the neck. Usually it is a steel bar or rod that runs inside the neck, beneath the fingerboard. Some are non-adjustable, but most modern truss rods have a nut at one or both ends that adjust its tension. The first truss rod patent was applied for by Thaddeus McHugh, an employee of the Gibson company, in 1921, though the idea of a "truss rod" appears in patents as early as 1908.