This is a horseradish root. It is something that used to be part of every meal containing red meat, but it has almost disappeared from the tables containing roasts, or steaks. We now eat it coloured lightly green and with our sushi. That's right, Horseradish root is wasabi.
This is horseradish root pealed. It is quite tough and strong smelling.
Cube it, and find a mask... if you think cutting onions is bad, wait until you grate horseradish root. I recommend you do it outside if possible, but a well ventilated room will do.
Grate it fine, add some salt (to taste, it varies from plant to plant) and enough cider vinegar to make it into a thick paste. Store in small jars in the fridge for a couple months. Serve this spicy condiment with your next pot roast, and bring a small jar over to grandma and grandpa and watch their excitement.