The term KEEP ___ ON (OBSERVE) can be completed with two words: TABS and ANEYE. The phrase 'keep tabs on' is an idiom that means to monitor or observe something closely. It is often used in the context of keeping track of someone or something, such as a person's progress or a situation. The phrase 'keep an eye on' is also an idiom that means to watch or observe something carefully. This phrase is often used to indicate that someone should pay attention to something or someone in order to ensure that nothing goes wrong.