The term 'with great speed' can be summarized by two crossword solutions: POSTHASTE (9 letters) and FAST (4 letters). POSTHASTE is an adverb meaning 'as quickly as possible' and is derived from the Middle English phrase 'post hast' which translates to 'go quickly'. FAST, on the other hand, is an adjective meaning 'moving or capable of moving at high speed' and is derived from the Old English word 'fæst' which means 'firmly fixed'.