The story
From gas + giant, coined by American science-fiction writer James Blish and first attested in 1952 in a rewritten version of his 1941 short story Solar Plexus.
Etymology from Wiktionary, CC BY-SA 4.0.
gas giant
Today it means: A large planet composed mostly of gaseous hydrogen and helium, along with methane and ammonia; possibly with a solid core. Full definition →