From The Online Merriam Webster Dictionary.

1 : not any thing : no thing <leaves nothing to the imagination>

Nothing has other senses that they list, but No. 1 seems to me to be applicable. Not Anything. If it is not anything then it is absolute nothing. I don't see that that is a problem. Nothing means just what it says, Not Anything, or an absence of anything, which would include any quantum foam that the universe might come from.

Just to restate it one more time for emphasis. Nothing means not anything, not space, not a quantum foam, not particles, not virtual particles, in other words Nothing.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.