The word "un heedful" means not paying attention or being careless. The antonyms of this word are razor-sharp, attentive, vigilant, keen, observant, watchful, diligent, mindful, cautious, and sensible. Being razor-sharp means being fully alert and focused. Being attentive is being careful, considerate, and mindful of one's actions. Vigilant is being watchful and alert to any potential danger or threat. Keen is being sharp and perceptive about a situation or event. Observant is being watchful and notice even the smallest details. Watchful is being alert and paying attention to any changes in the environment, while diligent is being persistent and hardworking. Mindful is being fully conscious and aware of what is happening in the present moment.