The use of the words "grave" and "genre" in a way of responding to questions and statements

Question

I admire this youtube channel for providing a lot of info on how to speak French, but just recently I was talking with my teacher and she said that I said something weirdly. We were supposed to pretend a conversation in a train. My friend and I were talking. He said:

• Le voyage a Paris, c'est long, hein?
• Grave! - I replied

And then my teacher was confused, because she said grave meant generally "heavy" and has no use in a sentence I wanted to use. She has also never heard of using "genre!" in order to express disagreeing. So... Is it a French slang? How do these words actually work?

Answer 1

Grave can have different meanings. In your quote it is an adverb used as an intensifier.

Le voyage a Paris, c'est long, hein ?
Grave!

Which could be translated in English as "indeed". Using grave this way is very colloquial, it would not be used in formal writing or spoken French.

An other use of grave as an intensifier:

Cette fille je l'aime grave.

Here it is used as an adverb. To stick to the colloquial register you could translate it as "I'm nuts about that girl".
This use of grave¹ is quite recent, it can have been around for about twenty or thirty years at most.

In formal language, the main use of grave is as an adjective meaning "serious", "heavy".

Il avait l'air grave et soucieux.

("he looked serious and worried.")

Ses blessures sont très graves.

("He's got some serious/heavy injuries.")

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^{1. Some examples here.}

Answer 2

you guess correctly, this is pure slang, mainly spoken by (those pretending to be) young people.

In this case grave would stand for

C'est gravement long !

which is not proper french either.

Answer 3

Those words are indeed French slang, mostly used by young people.

It's not surprising that teacher don't always know very colloquial language. They can be fluent in French, but if they don't regularly speak with young people they won't know the current slang. Once I used the term "viral video" during class and my English teacher corrected me and told me it didn't exist !

Answer 4

That's French slang mostly spoken by young people. That's quite common for some people (I use to say "grave").

"Grave" in your sentence has the same meaning as "Carrément" (= positive answer in which you show you completely agree).
You'll probably hear things like :

C'est grave bien !

But this isn't correct, even if young people talk like this. This not means you can't use it.
The meaning is still a strongly agreement, you insist on it. I think it comes from "Gravement", so it would means it would be a misusage:

Gravement:

• with a slow movement
• in a dangerous way
• with weightiness (I tried to translate to the best)

You mentionned "Genre" too.
Used in young's slang too. I think it is a contraction of "du genre", making it less weird to use in many sentences. You would understand it better as question:

-someone tells a story which is surprising
Genre ? (same as "du genre ?")

It means you ask for further explanation, or you're saying it like "No, really ?".
Tell your teacher about it, there are many words and expressions like that.