The antonyms for the word "un-observant" are numerous and often depend on the context in which the term is used. A person who is highly observant might be described as attentive, alert, or vigilant, while someone who is oblivious might be seen as careless, inattentive, or heedless. Other antonyms may include perceptive, astute, cognizant, or watchful, and some may even describe someone as hyper-aware or diligent. Regardless of the specific antonym used, the overall idea is that someone who is un-observant lacks the ability to pay attention or notice important details, while someone who is observant has a keen eye and is highly alert.