Wiktionary
n. (context astronomy English) A large planet composed mostly of gaseous hydrogen and helium, along with methane and ammonia; possibly with a solid core.
WordNet
n. any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter) [syn: Jovian planet]
Wikipedia
A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet", but in the 1990s it became known that Uranus and Neptune are really a distinct class of giant planet, being composed mainly of heavier volatile substances (which are referred to as 'ices'). For this reason, Uranus and Neptune are now often classified in the separate category of ice giants.
Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass. They are thought to consist of an outer layer of molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core. The outermost portion of their hydrogen atmosphere is characterized by many layers of visible clouds that are mostly composed of water and ammonia. The layer of metallic hydrogen makes up the bulk of each planet, and is referred to as "metallic" because the very large pressure turns hydrogen into an electrical conductor. The gas giants' cores are thought to consist of heavier elements at such high temperatures (20,000 K) and pressures that their properties are poorly understood.
The defining differences between a very low-mass brown dwarf and a gas giant are debated. One school of thought is based on formation; the other, on the physics of the interior. Part of the debate concerns whether "brown dwarfs" must, by definition, have experienced nuclear fusion at some point in their history.
Usage examples of "gas giant".
He was on the flight deck four hours into their spinup to the translation point to Tau Ceti System when the priority squirt came in from Uriel: five Ouster torchship-class destroyers had been hiding in the charged-particle dust torus of the inner moon of the outer gas giant and were now making a run toward their own translation points, using the G-type sun as a shield between them and the GIDEON Task Force.
Moldahar Effectuator had refueled by skimming a gas giant in the Epsilon Eridani System and was burning redder than usual.
But picking black holes out of the heart of a gas giant was evidently a bit too difficult, even for the humans of many millennia beyond my time.
What if we can move right past Earth, with its giant satellite and with its distant ringed gas giant, and never see any of it?
With it you could see the planets of the lesser sun, and even the gas giant that revolved around Juxt, the closest extrasystem star, almost a light-year away.
The image of the gas giant, growing visibly larger by the hour, did tend to be a distraction.