A plain in Mordor (LotR/636) translated “Plain of Ashes” (RC/457), a combination of lith “ash” and lad “plain” (SA/lith).
Conceptual Development: This name was already Lithlad “Plain of Ashes” when it first appeared in Lord of the Rings drafts from the 1940s (TI/208).
lith (“ash, sand, dust”) + lad (“plain, valley”)