A noun for “a plain” in the Quenya Verbal System (QVS) of the 1940s derived from ᴹ√LAD “lie flat, be flat” with variants landa and lanna (PE22/126), the latter probably derived from ✱ladna with the voiced stop d becoming a nasal before nasal n. It might simply be the noun form of adjective ᴹQ. landa “wide” from The Etymologies of the 1930s (Ety/LAD).
Neo-Quenya: For purposes of Neo-Quenya, I’d stick to the form landa, which appears in an inflected form landannar “to the plains” early in QVS (PE22/125).
A word for “sheet” in the Declension of Nouns (DN) from the early 1930s of unclear derivation.
Conceptual Development: In Early Qenya Word-lists of the 1920s, ᴱQ. talat was “dry land” (PE16/139). The word talat also appeared (unglossed) in notes on The Feanorian Alphabet from the mid-to-late 1930s (PE22/20).