A mark, object, or other indication of the existence or passing of something. A very small quantity, especially one too small to be accurately measured. A line or pattern displayed by an instrument using a moving pen or a luminous spot on a screen to show the existence or nature of something that is being investigated. The sum of the elements in the principle diagonal of a square matrix. Each of the two side straps, chains, or ropes by which a horse is attached to a vehicle that it is pulling. Find or discover by investigation. Copy (a drawing, map, or design) by drawing over its lines on a superimposed piece of transparent paper.