1. To remove something from a larger thing as a result of grinding, squeezing, or pressing. A noun or pronoun can be used between "mill" and "out." Healthier grains are those that do not have gotten the bran and germ milled out of them. We use a chemical process to mill the impurities out of the raw materials.
2. slang In trading card games, to have all of one's cards removed from play due to the actions of one's own or another player's card. A noun or pronoun can be used between "mill" and "out." I was nearly beaten in the game, but I managed to mill the other player out completely at the last moment. I was going to play my most devastating card on my next turn when she milled out my hand and won the game.
3. slang To severely harm or injure someone. A noun or pronoun can be used between "mill" and "out," but typically used in passive constructions. I nearly got milled out by a car on my cycle home last night.