Tolkien used a similar set of words for “forest” starting with the earliest versions of Elvish, but their derivation evolved somewhat over time. The earliest related root was ᴱ√TAVA “beam” with variant ᴱ√TAFA (the latter marked by Tolkien with a “?” and with no obvious derivatives) from the Qenya Lexicon of the 1910s as the basis for words like ᴱQ. taule “great tree”, ᴱQ. tauno “forest” and ᴱQ. tavar “dale-sprite” (QL/90). It also had derivatives in the contemporaneous Gnomish Lexicon such as G. tavros/G. taur “forest” and G. tavor “wood fay” (GL/69).
ᴱQ. taure “forest” did not appear as an independent word until drafts of the Oilima Markirya from around 1930 (PE16/62; MC/213). Thereafter Tolkien mostly stuck with Q. taurë and N./S. taur for “forest”. In The Etymologies of the 1930s Tolkien gave the root ᴹ√TAWAR “wood, forest” (Ety/TÁWAR), though in one place it was ᴹ√TAR (EtyAC/TUR). In notes associated with the Quendi and Eldar essay from 1959-60 Tolkien gave √TAWA “wood”, and in notes on “large & small” roots from 1968 Tolkien had √TAW “wood” (PE17/115).