A spike is a sharp point, often made of metal or wood, but not always. Hedgehogs have long skinny spikes that keep them from being eaten by predators.
The wide metal nails that fasten railroad ties to rails are called "rail spikes." A spike can be big like those rail spikes, or small like the ones on the bottom of a cleat. And, extremely high-heeled shoes are sometimes called "spike heels." When something increases and abruptly decreases, like the price of sugar or a fever, it spikes. To spike a volleyball, smash it over the net. Spike shares a root with the Latin spina, for "spine or thorn."