The antonyms for the word "nonobservant" are "observant," "watchful," "attentive," and "alert." These words describe a person who is keenly aware of their surroundings and actively pays attention to people, objects, and events. An observant person is attentive to detail and notices even the smallest changes or discrepancies. They are watchful and cautious, always on the lookout for any signs of danger or trouble. On the other hand, a nonobservant person is someone who overlooks details or doesn't pay attention to their surroundings. In general, being observant is a valuable trait that can help a person stay safe, avoid mistakes, and better understand the world around them.