This word appeared in The Etymologies of the 1930s as ᴹQ. talma “base, foundation, root” derived from ᴹ✶talmā, appearing under the root ᴹ√TALAM “floor, base, ground” as an extension of ᴹ√TAL “foot” (Ety/TAL). The word talma “basis” appeared as either a Quenya or a primitive word in Common Eldarin: Noun Structure from the early 1950s (PE21/80).
Conceptual Development: Qenya word-lists of the 1920s had ᴱQ. talma “end” (PE16/144). The Qenya Lexicon of the 1910s had ᴱQ. tauma “basis, foundation, ground floor” under the early root ᴱ√TAW̯A (QL/90).
Neo-Quenya: For purposes of Neo-Quenya I would use this word for “basis; foundation, base” (physical or conceptual), but for “root” I would use Q. sundo.
A variant of talan (talam-) “flat space, platform” in notes on Words, Phrases and Passages from the Lord of the Rings (PE17/52).
Neo-Quenya: I would not use this word for this purpose in Neo-Quenya, since elsewhere talma was used for “basis, base, foundation, root” (PE21/80; Ety/TAL).