The root ᴹ√TAY first appeared in The Etymologies of the 1930s with the gloss “extend, make long(er)” and derivatives like ᴹQ. taile “lengthening, extension”, ᴹQ. taina “lengthened, extended” and N. taen “long (and thin)” (Ety/TAY). Tolkien considered making it a variant of ᴹ√TAƷ (EtyAC/TAY), perhaps intending ᴹ√TAY to refer to horizontal length as opposed to vertical ᴹ√TAƷ. The root ᴹ√TAY “stretch” also appeared in the first version of Tengwesta Qenderinwa (TQ1) from the 1930s as the basis for ᴹ✶tainā “long”, and there were various related linguistic terms like Q. ómataima “vocalic extension” and Q. ómatailë “vowel lengthening” that appeared in both the first and second version of Tengwesta Qenderinwa (TQ1: PE18/34, 45; TQ2: PE18/86, 95).
The root √TAJA “stretch” appeared in notes associated with the Quendi and Eldar essay of 1959-60 (VT39/7), and √TAY “stretch” appeared in a list of sound roots from around this same time (PE17/138). However, in notes on the origin of the river name S. Taeglin “✱Boundary Singer”, Tolkien glossed √taya “mark, line, limit” with extension tayak as the basis for ✶taika “boundary, limit, boundary line” > S. taeg (WJ/309). Perhaps it was Tolkien’s intent that the sense “mark, line, limit” only applied to the extended form tayak.
This root was connected to fences, encirclement and rotation for much of Tolkien’s life. It first appeared as two distinct roots in the Qenya Lexicon of the 1910s. The first was ᴱ√PELE “fence in” with derivatives like ᴱQ. pelin “fenced in, pent”, ᴱQ. pelto “hedge, hedged field”, and ᴱQ. pelle “town” (QL/73). It had some clear derivatives in the contemporaneous Gnomish Lexicon such as G. pel “village”, G. pelu- “fence, enclose”, and G. pless “hedge, fence” (GL/64). The second root in the Qenya Lexicon of the 1910s was unglossed ᴱ√PELE with derivatives like ᴱQ. pelko “leg”, ᴱQ. pelte- “run”, and ᴱQ. peltas “pivot” (QL/73), but the “leg” word in the Gnomish Lexicon was unrelated: G. bactha “a leg” (GL/21).
Indeed, in Quenya the “leg” word was also shifted to a new root by The Etymologies of the 1930s: ᴹ√TELEK > ᴹQ. telko “leg” (Ety/TÉLEK). As for the root ᴹ√PEL, it was given the gloss “revolve on fixed point” in The Etymologies and seems to be a blending of 1910s ᴱ√PELE and ᴱ√PELE, with derivatives like ᴹQ. pel- “go round, revolve, return” and ᴹQ. peltas/N. pelthaes “pivot” (Ety/PEL) but also ᴹQ. peler/N. pêl “fenced field” and ᴹQ. opele/N. gobel “walled house or village, town” by way of extended root ᴹ√PEL(ES) (Ety/PEL(ES)).
The root √PEL appeared a number of times in Tolkien’s later writings with glosses like “edge, bound, fence, limit” (PE17/65), “fence, border” (PE17/90) and “go round, encircle” (SA/pel). Tolkien declared that:
> The basic sense should not be “revolve”; but “edge, bound, fence, limit”. Thus [S.] pelennor = fenced land; ephel, Sindarin < eppel < etpel = “outer wall or fence”; [Q.] peltakse- (peltas) should mean a fence of fixed stakes etc., or a “pale” and fencing stakes; and pelma a border, fringe, edge, limiting device (PE17/65).
Tolkien reassigned the sense “revolve” to the root √KWER. The most notable derivative of the new sense “boundary” for √PEL was Q. pella “beyond”, more literally “beyond the boundary” (PE17/65, 80); this word was likely Tolkien’s motivation for removing the sense “revolve” from √PEL.