Sindarin name of the river Hoarwell (LotR/200), also translated “Hoary Spring” (RC/15), a combination of mith “grey” and eithel “spring” (RC/772; SA/mith, eithel).
Conceptual Development: This name was already N. Mitheithel when it first appeared in Lord of the Rings drafts from the 1940s (TI/14).
mith (“grey”) + eithel (“spring, well”)