Hypersonic is a term used to describe speeds that are greater than five times the speed of sound. It is often used to refer to objects that travel at speeds of Mach 5 or higher. The two crossword solutions for this term are 'SPEEDY' (6 letters) and 'FAST' (4 letters). SPEEDY is an adjective that means moving quickly, while FAST is an adverb that means quickly. Both words accurately describe the speed of hypersonic objects.