The antonyms for the word "un energetic" are lively, energetic, vivacious, spirited, peppy, sprightly, active, dynamic, and vigorous. If someone is described as un energetic, they are considered to be dull, lethargic, and mellow. On the other hand, a person who is characterized as energetic has a strong enthusiasm and vigor for life, which feeds their lively personality. They are usually physically and mentally active, leading a dynamic life full of energy and excitement. In contrast, a person who is un energetic tends to be sluggish, quiet, and uninterested in most things around them. Therefore, it is always better to be lively and energetic than to be un energetic.