In his seminal satirical masterpiece Gulliver's Travels, Jonathan Swift wrote about a fictional land inhabited by giants that protagonist Lemuel Gulliver visits after his second shipwreck. This land was named Brobdingnag, but in the preface to that section of the novel, Gulliver complains that the correct spelling is actually Brobdingrag and that the publisher messed up in editing the word. This adds a bit of verisimilitude to the narration and makes it seem more like an actual account. The word seems to have been randomly chosen to just sound sort of big. The book was published in 1726, and, according to the Oxford English Dictionary, the word Brobdingnagian developed as an adjective meaning by 1731 (noticeably without the "correct" r). It peaked in usage in the 1930s and has generally levelled off since.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.