verb (v)

• lessen the density or solidity of(verb.change)

  source: wordnet30
• make more subtle or refined(verb.change)

  Synonym:
  sublimate, subtilize
  

  source: wordnet30
• weaken the consistency of (a chemical substance)(verb.change)

  Synonym:
  attenuate
  

  source: wordnet30
• To make rare, thin, porous, or less dense; to expand or enlarge without adding any new portion of matter to; -- opposed to condense.(verb)

  source: webster1913
• To become less dense; to become thin and porous.(verb)

  source: webster1913