If you're talking about the word boost that is about speed, its opposite is slow down. But if you're talking about the literal or real meaning of boost (which means increase), the opposite word of that is reduce, decrease or lessen.
Meaning of this word is "removing something". This is the real meaning of that word. It is used sometimes in normal talking.
A word meaning at a dangerous speed that starts with break is BREAKNECK. Meaning = (prenominal) (of speed, pace, etc.) excessive and dangerous. Hoped that helped. :)
fast
One possibility is that it stands for the Latin word "celeritas" meaning speed.
The meaning of the word haste is commonly accepted to be a movement with excessive speed or urgency. Some synonyms of the word haste include hurry, rush and speed.
Tempo?
S is for speed.
the word present is a multi meaning word so it depends which definition that you are talking about.
Tempo
Speed and direction of an objects motion.
S is for speed.