The opposite or antonym of the word "un-vigilant" is "vigilant." Vigilant refers to being alert and watchful, especially to detect danger, risks or threats. Other antonyms for un-vigilant include attentive, aware, observant, alert, cautious, guarded, watchful, mindful and vigilant. Being vigilant is essential for personal safety or security, monitoring and oversight, crime prevention, and other situations that involve risk management. By contrast, being un-vigilant implies carelessness, inattentiveness, or lacking awareness of a situation. It is important to be aware of the opposite meanings of words to better understand the nuances of language and communication.