A noun for “floor” in The Etymologies of the 1930s, an elaboration of N. pân “plank” under the root ᴹ√PAN (Ety/PAN). As such, it likely refers to a constructed floor made of wood or other materials.
Conceptual Development: The Gnomish Lexicon of the 1910s had G. blath “a floor” (GL/23), probably derived from the early root ᴱ√PALA having to do with flat things as suggested by Christopher Tolkien (LT1A/Palúrien).
A noun in The Etymologies of the 1930s glossed “ground, floor” derived from the root ᴹ√TALAM “floor, base, ground” (Ety/TAL). It has a plural form teleif in keeping with Noldorin plural patterns; in Sindarin its plural would be ^telaif. Its Quenya cognate was ᴹQ. talan, and in later writings this pair became Q. talan/S. talan “flat space, platform” < √TALAM (PE17/52), both demonstrating the ancient sound change whereby [[p|final [m] became [n]]] (VT47/24).
Neo-Eldarin: In later writings, S. talan was used mainly to refer to an elevated platform or floor, such as the flets of Lothlórien. As such, I think it is worth retaining talaf to refer both to the ground floor as well as the ground itself, perhaps from a variant ancient form ✱talamē.