The phrase "slacken pace" means to slow down or reduce speed. The opposite of this phrase would be to "increase pace" or to "speed up." Other antonyms for "slacken pace" include "hurry," "rush," "accelerate," "pick up speed," "hasten," and "quickly move." These words denote a sense of urgency and are often used when time is of the essence. For example, athletes might "increase pace" to catch up to an opponent, workers might "hurry" to meet a deadline, or drivers might "accelerate" to merge onto a busy highway. Whatever the context, antonyms for "slacken pace" suggest a need for action and quick movement.