Noun
a slender magnet suspended in a magnetic compass on a mounting with little friction; used to indicate the direction of the earth's magnetic pole
Source: WordNetThe magnetic needle is free to rotate in the horizontal plane. Source: Internet
He showed that a magnetic needle, made to oscillate over nonferrous surfaces, such as water, glass, copper, etc., falls more rapidly in the extent of its oscillations according as it is more or less approached to the surface. Source: Internet