Neptune

noun

Nep·​tune ˈnep-ˌtün 

-ˌtyün

1

a

: the Roman god of the sea compare poseidon

b

: ocean

2

: the planet eighth in order from the sun see Planets Table

Neptunian

nep-ˈtü-nē-ən 

-ˈtyü-

adjective

Synonyms

• blue
• brine
• deep
• ocean
• sea
• seven seas

Examples of Neptune in a Sentence

sailors shipwrecked by the wild waves of Neptune

Recent Examples on the Web

The planet’s large size – with a radius 2.6 times that of Earth – means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, according to astronomers. —Eric Lagatta, USA Today, 19 Apr. 2025

The love planet will also conjunct Neptune on May 2, adding a magical, almost surreal quality to these connections. —Valerie Mesa, People.com, 19 Apr. 2025

Astronomers think that this world could either be a smaller version of our solar system’s ice giant Neptune, called a mini-Neptune, or perhaps a rocky planet with no water but a massive hydrogen atmosphere, called a gas dwarf. —Daniel Apai, The Conversation, 18 Apr. 2025

The exoplanet’s size appears to be between that of Earth and Neptune and belongs to a range that scientists have never seen up close. —Meghan Bartels, Scientific American, 17 Apr. 2025

Word History

Etymology

Latin Neptunus

First Known Use

before the 12th century, in the meaning defined at sense 1a

Kids Definition

Neptune

noun

Nep·​tune ˈnep-ˌt(y)ün 

: the planet eighth in order from the sun see planet

Neptunian

nep-ˈt(y)ü-nē-ən 

adjective