quand tous les gros gras grands grains d’orge
Fernando Botero The Beach
So now just for fun – here is a very famous exercise of pronunciation (called “un virelangue”).
I would never say to describe a friend “il est gros” or “elle est grosse”, it’s kind of mean. In this situation, French likes to use a negative construction: “elle n’est pas mince” = she is not thin. We’d also say “il est bien en chair”, which literally translated in “he is well in flesh”. See below for more info with the use of our third adjective: “gras, grasse”.
se dégros gras grand grain d’orgeront.
I would use “gros/grosse” for someone I don’t know, or to describe myself, specially if I’m fishing for compliments:
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Finally, of course “gros” in French doesn’t mean “gross” in English: use “dégoûtant” (disgusting).
If you think of more useful idioms using gros/grand/gras, list them in the comments and I’ll add them to the article -merci !