Weightless

That's correct. In Japanese, ウエートレス corresponds both to the English "waitress" and "weightless". However, "waitress" is the more usual meaning.

That's right. In Japanese, "uetoresu" corresponds both to the English "waitress" and "weightless". However, "waitress" is the more common meaning.

Astronauts are weightless and can sleep in any orientation. However, they have to attach themselves so they don't float around and bump into something.

An astronaut in space can be weightless but cannot be without mass.

Heating boils off the liquid in the gel and the material that remains is like a hard sponge, slightly coarse and almost weightless.