What word names the plectrum of a harpsichord and a porcupine's spine?

What is a play area for very young children, and also a franchised children's TV show begun in 1953? What is a playing card with two spots called? Which playwright wrote the line "We are all born mad. Some remain so"? A plaza in San Francisco is named for which politician, a city supervisor when he was slain in 1978? A plow appears on the seal of which Cabinet department created in 1862? What is a plum that has been dried called? A plumber uses which long, flexible tool, named for an animal, to clear your pipes? A plump, bearded Dutchman who drove him by sleigh on December 24, 1822, reputedly inspired which man's famous poem?