(astronomy) The eighth planet in our solar system, represented in astronomy and astrology by ♆. / (Roman mythology) The god of the ocean and of earthquakes. The same as Poseidon in Greek mythology.

(historical) A discredited scientific theory of geology, held by many scientists around the late 18th century and early 19th century, that rocks were formed from the crystallisation of minerals in the early Earth's oceans.

(inorganic chemistry) Relating to trivalent neptunium

(inorganic chemistry) Any oxyanion of neptunium; any salt containing such an ion

(inorganic chemistry) Relating to tetravalent neptunium.

plural of neptunate

Posidonia oceanica, a seagrass native to the Mediterranean.

plural of hot Neptune

A large cup-shaped marine sponge (Cliona patera).

An explosive containing nitroglycerine, used in blasting.