To oxygenate something is to put oxygen into it, or to raise how much oxygen it holds. Doctors oxygenate blood when a patient’s lungs cannot do that job well; the blood still needs oxygen to carry around the body. You oxygenate water in a fish tank with a pump and bubbles, so the fish can breathe. Some factories oxygenate drinks. The -ate ending makes a verb from oxygen: “to give it oxygen.” Oxygenated blood is bright; blood that has given its oxygen away is darker. This is mostly medicine, science, and technical English. Everyday talk more often just says “add oxygen” or “put air in.”