The Collaborative International Dictionary of English v.0.48:

Proteus \Pro"te*us\, prop. n. [L., Gr. ?.]
   1. (Class. Myth.) A sea god in the service of Neptune who
      assumed different shapes at will. Hence, one who easily
      changes his appearance or principles.
      [1913 Webster]

   2. (Zool.) A genus of aquatic eel-shaped amphibians of the
      family Proteidae of the order Urodela, found in caves
      in the karst regions near the Adriatic from Trieste to
      Montenegro (including Slovenia, Croatia, and Herzegovina);
      also called the Olm, White Salamander, and Human
      fish; it is a true troglobiont (cave animal). They have
      permanent external gills as well as lungs. The vestigial
      eyes are small and can only perceive light and dark; the
      legs are weak. Some were reported in Germany and France,
      apparently due to human intervention. It was known to
      Charles Darwin who wrote about cave animals in The Origin
      of Species, chapter 5.
      [1913 Webster + PJC]

            The unusual Olm (Proteus anguinus, aka Cave
            Salamander, although no relation to the
            Hydromantes spp) is the only European member of
            the Proteidae family, the rest occurring in
            America. This species was only discovered in 1875
            and even today is only known in about fifty caves in
            the limestone mountains of the region, plus one
            isolated location in Italy. Olms are characterised
            by an elongated body, white unpigmented skin, three
            pairs of external gills and vestigial, skin-covered
            eyes which can only perceive light and shadow. The
            Olm hunts aquatic crustaceans such as water fleas
            mainly by sensory organs in the skin. If washed out
            of their caves by heavy rainfall, olms will collect
            in deep pools, but they will not voluntarily leave
            the water. At the same time they have lungs and
            drown if they cannot surface at some point for air.
            The optimum water temperature for this species is
            5-10 C. Females normally give birth to two larvae,
            but curiously enough if the water is warm enough
            (about 15 deg C) they can lay up to 80 eggs instead.
            A lot is still undiscovered about the lives of these
            mysterious creatures.
      --http://www.nafcon.dircon.co.uk/euro_urodela.html
      [PJC]

   3. A changeable protozoan; an amoeba.
      [1913 Webster]

   4. A genus of gram-negative rod-shaped bacteria, including
      some species pathogenic in man.
      [PJC] Prothalamion

WordNet (r) 3.0 (2006):

Proteus
    n 1: (Greek mythology) a prophetic god who served Poseidon; was
         capable of changing his shape at will
    2: type genus of the Proteidae [syn: Proteus, genus Proteus]

The Free On-line Dictionary of Computing (30 December 2018):

PROTEUS

   An extensible language, the core of PARSEC.

   ["The Design of a Minimal Expandable Computer Language",
   J.R. Bell, PhD Thesis, CS, Stanford University (Dec 1968)].