Being vigilant refers to staying alert, watchful, and guarded. Antonyms for this term can mean the opposite, indicating a lack of attention or awareness. Synonyms of these antonyms may include being forgetful, careless, unobservant, and inattentive. For instance, negligence, nonchalance, laxness, and unconcern are few of the antonyms for being vigilant. When someone is not vigilant, they may not notice potential problems, threats, or dangers, which can lead to a lack of safety and security. Therefore, it's essential to be vigilant and alert at all times, especially in situations where safety is a concern.