[djur]

What does "very fast" actually convey that "fast" doesn't, unless you have a specific example of "fast" to compare with?

The idea isn't that "rapid" means "very fast" (I don't think it even necessarily means faster than "fast"). It's that people will use "very fast" when they feel that "fast" lacks the punch the sentence needs, even when they don't actually mean anything different from "fast".

[gpm]

You're narrowing the range of things that you're describing to not include "normal fast". This can be useful for a variety of reasons. You might be instructing people to skate extra fast this game, while avoiding implying that they usually don't meet the criteria of the word fast. You might be acknowledging that coup is a fast board game, but saying you only have time for an unusually short round of coup (even for coup) before you need to leave.

To quote the person I initially responded to

> However, if there is an opportunity to be more exact, one should take it without remorse.

That is what "very fast" commonly does over "fast". It costs next to nothing, and it specifies the meaning slightly more precisely.

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I don't think "rapid" is really a convincing alternative to "very fast" in any case where the "very" is warranted. I liked the "breakneck" suggestion by the site a bit more, but in most contexts I don't think that it's better, just different.