adjective (a)

• relating to or characteristic of animals of the class Amphibia(adj.pert)

  Synonym:
  amphibian
  

  source: wordnet30
• operating or living on land and in water(adj.all)

  Example:
  Amphibious vehicles.
  Amphibious operations.
  Amphibious troops.
  Frogs are amphibious animals.
  

  Antonym:
  terrestrial
  

  source: wordnet30
• Having the ability to live both on land and in water, as frogs, crocodiles, beavers, and some plants.(adjective)

  source: webster1913