Súlë
From Tolkien Gateway
súlë is a noun meaning "spirit" in Quenya. Compare with fëar in Sindarin.
Súlë is also the name of the ninth letter of the Tengwar alphabet.
History
The original name of Súlë was Thúlë and in Quenya it had the value "th". Over time the "th" in Quenya mutated to "s" and the letter was renamed Súlë.