Animals living on land and in water

One word substitute is Amphibian.

Ambiguous: open to more than one interpretation; not having one obvious meaning.
Amphibian: a cold-blooded vertebrate animal of a class that comprises the frogs, toads, newts, salamanders, and caecilians. They are distinguished by having an aquatic gill-breathing larval stage followed (typically) by a terrestrial lung-breathing adult stage.
Amorphous: without a clearly defined shape or form.
Ambivalent: having mixed feelings or contradictory ideas about something or someone.