great circle (aerial navigation). A circle formed on the surface of a sphere in such a way that the plane of the circle passes through the center of the sphere. All meridians of longitude on the earth’s surface are great circles, but the equator is the only parallel of latitude that is a great circle.
great circle course (navigation). The route between two points on the earth’s surface measured along the shorter segment of the circumference of the great circle on which the two points are located. A great circle course establishes the shortest distance over the surface of the earth between any two terrestrial points.
green run (aircraft manufacturing operation). The first time an engine is run in the process of aircraft manufacturing or major overhaul.
Greenwich mean time. Mean solar time at the 0° meridian, the meridian of longitude that passes through the Royal Observatory in London, England. Greenwich mean time (GMT) is also known as Zulu time and Universal time.
greige (pronounced gray). The unshrunk condition of a polyester fabric as it is removed from the loom. The material has not been bleached, dyed, or shrunk.
grid (electron tube component). The electrodes in an electron tube between the cathode and the anode. Grids are used to control the amount, the shape, and the velocity of the stream of electrons between the cathode and the anode.
grid dip meter (electrical measuring instrument). An electronic instrument used to find the resonant frequency of an inductive-capacitive (LC) tuned circuit. The grid dip meter contains a variable-frequency oscillator and an indicating instrument. The probe of the grid dip meter is held near the circuit being examined, and the oscillator is tuned until the meter dips. The frequency produced by the oscillator when the meter dips is the resonant frequency of the circuit.
grinder (power tool). A power tool using an electric motor to drive an abrasive wheel. Grinders are used to sharpen tools and to grind away or shape metal parts.
grip length (threaded fastener specification). The thickness of material a fastener is designed to fasten, or hold together. The grip length of a bolt is the length of the unthreaded portion of the shank.

grip range (special rivet specification). The difference between the minimum and maximum thickness of material a special rivet can be used to fasten.
grit blasting. Another name for abrasive blasting. See abrasive blasting.