Not so fast! Take a break to read this article on word grammar by Tim Bowen.
Apart from its more common uses as an adjective or an adverb, the word fast can also function as a noun and a verb.
A fast is a period of time when you eat no food or very little food, usually for religious reasons. The verb to fast means that you abstain from eating for a period of time, as in 'Muslims fast from sunrise to sunset during Ramadan'.
As an adjective, fast has a couple of other meanings apart from the main one of ‘able to move quickly’. Fast colours are ones that do not normally fade when clothes are washed.
If a clock or watch is fast, it shows a time that is later than the correct time. In this use, fast cannot be used before the noun. However, in the expression fast film, referring to film that is used to take pictures of something that is moving quickly or when there is not much light, fast is used before the noun.
If you make something (hold/stick) fast, you fix it securely so that it cannot move, as in ‘They put the rope around a post and made it fast'.
Fast is also used in the expression fast and furious to describe a situation in which a lot of different things happen one after the other, as in ‘Political changes have been fast and furious since the coup’.
Apart from its use to mean quickly, the adverbial form of fast can also be used to mean firmly and strongly or tightly, as in 'The van was stuck fast in the mud' or 'She held fast to the railings and refused to move'.
It is also used in the expression fast asleep, meaning 'sleeping in a way that makes it difficult to wake you' and in the spoken expression 'Not so fast', which is used to tell someone to wait and not to be too quick to do something.