Finnegan pin n. a non-existent part or tool; a thing whose name is forgotten or unknown; a doo-dad or thingamajig. (source: Double-Tongued Dictionary)
Further reading
We tend to take the index of a book for granted, but centuries ago, these helpful lists were viewed with suspicion. Some even worried that indexes would harm reading comprehension! A witty new book tells the story. Plus, the Latin term bona fides...
We use the term Milky Way for that glowing arc across the sky. But how people picture it varies from culture to culture. In Sweden, that starry band goes by a name that means “Winter Street,” and in Hawaii, a term for the Milky Way...