The term "slacks off" refers to a behavior that means to reduce one's effort or energy. Antonyms for "slacks off" are words that describe behaviors that are opposite to this term. The antonyms of "slacks off" can be words like "perseveres," "works hard," "diligent," or "consistent." These words describe behaviors that help people to maintain their focus and work diligently towards their goals without being lenient. When someone doesn't "slack off," they tend to accomplish more and achieve their goals efficiently. Some of the synonyms of antonyms for "slacks off" include determined, energetic, and focused, indicating that people should strive to stay motivated and avoid becoming lethargic or complacent in their endeavors.