adjective (a)

• (of a substance) capable of being dissolved in some solvent (usually water)(adj.all)

  Antonym:
  indissoluble, insoluble
  

  source: wordnet30
• susceptible of solution or of being solved or explained(adj.all)

  Example:
  The puzzle is soluble.
  

  Antonym:
  insoluble
  

  source: wordnet30
• Susceptible of being dissolved in a fluid; capable of solution; as, some substances are soluble in alcohol which are not soluble in water.(adjective)

  source: webster1913