Increasing speed is the antonym for the phrase "reduces speed." It refers to the action of accelerating the speed of any object or mechanism. Other antonyms for reduce speed include amplifying, escalating, hastening, and advancing. These words often imply an increase in velocity and motion. Conversely, reducing slowdown can be achieved by decelerating, slowing down, hindering, or braking. All these antonyms suggest a decrease or a decrease in velocity or movement. Therefore, antonyms for reducing speed can be crucial when describing the acceleration or deceleration of an object, a vehicle, or any movement in a given scenario.