NOUN (2)

1. (Roman mythology) god of the sea; counterpart of Greek Poseidon;

2. a giant planet with a ring of ice particles; the 8th planet from the sun is the most remote of the gas giants;
- Example: "the existence of Neptune was predicted from perturbations in the orbit of Uranus and it was then identified in 1846"

The Collaborative International Dictionary of English v.0.48:

Neptune \Nep"tune\, prop. n. [L. Neptunus.]
   1. (Rom. Myth.) The son of Saturn and Ops, the god of the
      waters, especially of the sea. He is represented as
      bearing a trident for a scepter.
      [1913 Webster]

   2. (Astron.) The remotest major planet of our solar system,
      discovered -- as a result of the computations of
      Leverrier, of Paris -- by Galle, of Berlin, September 23,
      1846. It is classed as a gas giant, and has a radius of
      22,716 km and an estimated mass of 1.027 x 10^26 kg,
      with an average density of 2.27 g/cc. Its mean distance
      from the sun is about 5,000,000,000 km (3,106,856,000
      miles), and its period of revolution is about 164.78
      years.
      [1913 Webster +PJC]

   Neptune powder, an explosive containing nitroglycerin, --
      used in blasting.

   Neptune's cup (Zool.), a very large, cup-shaped, marine
      sponge (Thalassema Neptuni).
      [1913 Webster]

WordNet (r) 3.0 (2006):

Neptune
    n 1: (Roman mythology) god of the sea; counterpart of Greek
         Poseidon
    2: a giant planet with a ring of ice particles; the 8th planet
       from the sun is the most remote of the gas giants; "the
       existence of Neptune was predicted from perturbations in the
       orbit of Uranus and it was then identified in 1846"

Moby Thesaurus II by Grady Ward, 1.0:

151 Moby Thesaurus words for "Neptune":
   AB, Agdistis, Amor, Ancient Mariner, Aphrodite, Apollo, Apollon,
   Ares, Argonaut, Artemis, Ate, Athena, Bacchus, Ceres, Cora, Cronus,
   Cupid, Cybele, Davy, Davy Jones, Demeter, Despoina, Diana,
   Dionysus, Dis, Dylan, Earth, Eros, Flying Dutchman, Gaea, Gaia, Ge,
   Great Mother, Hades, Helios, Hephaestus, Hera, Here, Hermes,
   Hestia, Hymen, Hyperion, Jove, Juno, Jupiter, Jupiter Fidius,
   Jupiter Fulgur, Jupiter Optimus Maximus, Jupiter Pluvius,
   Jupiter Tonans, Kore, Kronos, Magna Mater, Mars, Mercury, Minerva,
   Mithras, Momus, Nereid, Nereus, Nike, OD, Oceanid, Oceanus,
   Olympians, Olympic gods, Ops, Orcus, Persephassa, Persephone,
   Phoebus, Phoebus Apollo, Pluto, Poseidon, Proserpina, Proserpine,
   Rhea, Saturn, Tellus, Thetis, Triton, Uranus, Varuna, Venus, Vesta,
   Vulcan, Zeus, able seaman, able-bodied seaman, asteroid,
   bluejacket, buccaneer, deep-sea man, fair-weather sailor,
   fisherman, fresh-water nymph, hearty, inferior planet, jack,
   jack afloat, jack-tar, jacky, kelpie, limey, limniad, lobsterman,
   major planet, man fish, mariner, matelot, mermaid, merman,
   minor planet, naiad, navigator, nix, nixie, ocean nymph, pirate,
   planet, planetoid, privateer, sailor, salt, sea devil, sea dog,
   sea god, sea nymph, sea rover, sea-maid, sea-maiden, seafarer,
   seafaring man, seaman, secondary planet, shipman, siren,
   solar system, superior planet, tar, terrestrial planet, undine,
   viking, wanderer, water dog, water god, water spirit, water sprite,
   whaler, windjammer, windsailor



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

Neptune

   A hypertext system for computer assisted software engineering,
   developed at Tektronix.