A noun for “ash” appearing as an element in names like Lithlad “Plain of Ashes” (RC/457) and Dor-nu-Fauglith “Land under Choking Ash” (WJ/239-240), as well as in the adjective lithui “ashy, ashen” (RGEO/66, RC/765). It is translated as “dust” in the name Anfauglith “Gasping Dust” (S/150), but since this is the name for Ard-galen after the region was burned by the forces of Morgoth, this may simply be a loose translation for “ash”.
Conceptual Development: In The Etymologies of the 1930s N. lith was glossed “sand” from primitive ᴹ✶litse under the root ᴹ√LIT (Ety/LIT), and in this document N. Fauglith was translated “Thirsty Sand” (Ety/PHAU), as opposed to its original translation from the 1920s and early-to-mid 1930s which was simply “Thirst” (LB/275; SM/26, 101; LR/280).
Neo-Sindarin: For Neo-Sindarin I’d use lith mainly in its 1950s-60s sense “ash” but also allow its 1930s sense “sand”, but for “dust” I’d use [N.] ast. @@@ Maybe it would be better to coin a neologism for “sand”?