vaporous

1. Relating to or resembling vapor.
2. 1. Producing vapors; volatile.
   2. Full of vapors.
3. Insubstantial, vague, or ethereal: "the imponderable mysterious and vaporous illusions of twilight" (John C. Powys). See synonyms at airy.
4. Extravagantly fanciful; high-flown: vaporous conjecture.

adjective

So light and insubstantial as to resemble air or a thin film: aerial, aery, airy, diaphanous, ethereal, filmy, gauzy, gossamer, gossamery, sheer², transparent, vapory. See thick/thin.

The adjective has 3 meanings:

Meaning #1: so thin as to transmit light
  Synonyms: diaphanous, filmy, gauzy, gossamer, see-through, sheer, transparent, cobwebby

Meaning #2: resembling or characteristic of vapor
  Synonyms: vaporific, vaporish, vapourish

Meaning #3: filled with vapor
  Synonyms: miasmal, miasmic