Get going, stop delaying. Lead being a heavy material, the source of this expression, usually an imperative (“Get the lead out of your feet!”), seems fairly clear. There are numerous variants for “feet,” mostly less polite (pants, britches, ass, butt), and shake is sometimes substituted for “get.” It is also sometimes shortened to simply get the lead out. The term originated in America in the first half of the twentieth century and became widely used in the armed services during World War II.