LEAD (6)

Lead (?), n. 1. 1. (Music.) (a) The announcement by one voice part of a theme to be repeated by the other parts. (b) A mark or a short passage in one voice part, as of a canon, serving as a cue for the entrance of others.
2. 2. In an internal-combustion engine, the distance, measured in actual length of piston stroke or the corresponding angular displacement of the crank, of the piston from the end of the compression stroke when ignition takes place; — called in full lead of the ignition. When ignition takes place during the working stroke the corresponding distance from the commencement of the stroke is called negative lead.
3. 3. (Mach.) The excess above a right angle in the angle between two consecutive cranks, as of a compound engine, on the same shaft.
4. 4. (Mach.) In spiral screw threads, worm wheels, or the like, the amount of advance of any point in the spiral for a complete turn.
5. 5. (Elec.) (a) A conductor conveying electricity, as from a dynamo. (b) The angle between the line joining the brushes of a continuous-current dynamo and the diameter symmetrical between the poles. (c) The advance of the current phase in an alternating circuit beyond that of the electromotive force producing it.
6. 6. (Theat.) A rôle for a leading man or leading woman; also, one who plays such a rôle.