Definition: Silmaril: A fictional, magical substance found deep underground in the Mines of Gondor. It powers the Ring in The Lord of the Rings series. Detailed Definition: Silmaril is a fictional substance that powers the Ring in J.R.R. Tolkien's epic fantasy series, The Lord of the Rings. This substance can grant its holder extraordinary abilities like invisibility and magical enhancements. Is there anything specific you'd like to know or learn about the word?