Tolkien used a number of similar roots as the basis for “line” words throughout his life. The earliest of these appeared in the Qenya Lexicon as ᴱ√TEHE [teχe] “pull” (gloss marked with a “?” by Tolkien) with derivatives like ᴱQ. tea “straight”, ᴱQ. telya “attractive; importunate”, and ᴱQ. tie “line, direction, route, road” (QL/90), the last of these surviving more or less unchanged all the way into the published version of The Lord of the Rings (LotR/377). The early root ᴱ√TEHE also had derivatives in the contemporaneous Gnomish Lexicon such as G. tê “mark, line; track; path”, G. tî or tion “straight”, and G. tîr “honest; esteem, regard, honour”, originally “straight, upright” (GL/69, 71). Primitive ᴱ✶tegna > ᴱQ. tína/ᴱN. tain “straight” from Early Noldorin Word-lists from the 1920s may represent a shift in the form of the root to ✱ᴱ√TEGE (PE13/153, 165).
In The Etymologies of the 1930s the root appeared as {ᴹ√TEƷ >>} ᴹ√TEÑ “line, direction” with derivatives like ᴹQ. tie/N. tê “line, way” and ᴹQ. téra/N. tîr “straight, right” (Ety/TEƷ, TEÑ). In the Outline of Phonology Tolkien gave √TEG “line”, whereas √TEÑ was given as the basis for Q. tenna “a thought, notion, idea” and thus clearly with a different meaning; see the entry √TEÑ for further discussion. In any case it is clear that Tolkien considered various ancient velar consonants for the second consonant of this root, all ultimately vanishing in the child languages with similar vocalic effects: 1910s teχ-, 1920s teg-, 1930s {teʒ- >>} teñ- and 1950s teg-.
A variant of √LED in notes from the late 1950s or early 1960s that Tolkien considered to explain the derivation of S. lembas “waybread” (PE17/60). The root ᴹ√LEN “(?road), way” also appeared earlier in The Etymologies of the 1930s as the basis for N. lembas (EtyAC/LEN). Tolkien may have settled on this root when he revised the earlier root ᴹ√LED (Ety/LED) “go, fare, travel” >> √DEL “walk, go, proceed, travel” in the 1959-60 Quendi and Eldar essay (WJ/360), deciding that its inversion √LED was used mainly in Quenya (WJ/363).
A possible precursor to this root is ᴹ√LĒ “go, fare” in the Declension of Nouns (DN) from the early 1930s with derivative ᴹQ. lesto “journey” (PE21/12). This is turn is probably a later iteration of ᴱ√LEHE “come, be sent, approach” from the Qenya Lexicon of the 1910s, given as a variant of ᴱ√ELE (QL/52). It is probably the basis for contemporaneous G. len “come, arrived” and G. lentha- “come towards speaker, approach, draw near” (GL/53) and possibly ᴱQ. lehe- or ᴱQ. lehta- “ride” from the English-Qenya Dictionary of the 1920s (PE15/76).
For a discussion of other parallel roots, see √LED and √DEL.