The antonyms of the word 'hyper sonic' are slow, sluggish, lethargic, and dull. 'Hyper sonic' refers to speeds that are extremely high and surpass the speed of sound, whereas its antonyms refer to languid and slow movements. The term 'hyper sonic' is often used to describe modern military technology, such as missiles or airplanes, that can travel at tremendous speeds. Conversely, the antonyms of 'hyper sonic' are used to describe the lack of speed, energy, or excitement. In conclusion, the antonyms of 'hyper sonic' are words that represent the opposite of high speed and rapid movements.