While the adjective torpid sounds a lot like the noun torpedo, it actually describes something slow or even inactive, like the torpedo that's just sitting around before it's launched.
Torpid comes from the Latin word torpere, meaning "numb," which is exactly how torpid things act. A hibernating bear and a caterpillar holed up in a cocoon are two good examples. You might feel torpid sitting in front of the fire after a big meal. The mind, too, can become torpid. The writer Samuel Johnson said, “It is a man’s own fault, it is from want of use, if his mind grow torpid in old age.”