elephant
n.— «Vale threw a party in Ulan Bator with samba dancers flown in from Brazil to mark the company’s arrival in Mongolia to search for another “elephant”—mining parlance for a big discovery.» —“Ivanhoe Seeks Riches Selling Output of Mongolian Mine to China” Bloomberg.com Oct. 27, 2004. (source: Double-Tongued Dictionary)
Further reading
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...