Qenya
landa
noun. plain
landa
adjective. wide, wide, [ᴱQ.] broad
lanna
noun. plain
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
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).