This root first appeared in the Qenya Lexicon of the 1910s as ᴱ√TENE “touch, feel”, with derivatives like ᴱQ. tende “sense of touch, sense, sensation, feeling” and ᴱQ. tenya- “feel, touch” (QL/91). G. tent “toe” and G. tentha- “feel with the feet, walk on tiptoe” from the contemporaneous Gnomish Lexicon might be related (GL/70). There were then no further signs of this root for many years, except perhaps the preposition ᴹQ. ten “for” in Fíriel’s Song of the 1930s.
The root √TEN “direction” eventually reappeared in Quenya Notes (QN) from 1957 with a single derivative, adverb or preposition Q. tenna “to the object; up to, to (reach), as far as”, as in the phrase Q. tenn’ Ambar-metta “unto the ending of the world” (LotR/967). The root √TEN also appeared with gloss “end in sense of point aimed at” (vs. √MET = “finally”) along with derivatives Q. tenna “to the point, until” and Q. †tenya- “arrive, end (not at speaker’s[?] place)” in notes from the late 1950s or early 1960s (VT49/24).
In notes from 1968, √TEN was at first used for “to, arrive (at), reach” along with derivatives Q. tenna “right up to a point (of time/place); go as far as” and a verb Q. ten- “arrive, come to”, but then Tolkien changed {√TEN >>} √MEN and revised all the verb forms of {Q. ten- >>} men- (VT49/23-24). He then gave a new gloss “point” to √TEN and updated derivatives: Q. tenna “to the point” and Q. tenta- “point to, [point] out, indicate” (VT49/24). In another note associated with 1968 drafts of the Ambidexters Sentence, the root √TEN was glossed “toward” (VT49/24).
Neo-Eldarin: For purposes of Neo-Eldarin, I’d ignore Tolkien’s brief interpretation of this root as “arrive”, and stick with the meaning “(up to the) point”, consistent with its non-deleted derivatives. For “arrive”, I’d use Q. anya- from Late Notes on Verbs written in 1969, reserving √MEN for “go” (LVS).
A root Tolkien introduced in the late 1960s as the basis for his latest Elvish word for “ten”: Q. quëan/quain, S. pae, T. pai(n) (VT42/24; VT48/6). It was an extension of √KWA “complete” as in “a complete set of (10) fingers”. Prior this late change, the usual word for “ten” was ᴹQ. kainen (along with other variants beginning with kai- or kea-) from the root ᴹ√KAYAN or ᴹ√KAYAR as it appeared in The Etymologies of the 1930s (Ety/KAYAN). This basis for “ten” dates back to the Early Qenya Grammar of the 1920s (PE14/49, PE14/82). Tolkien was still considering √KAYAN for “10” in the late 1960s before replacing it with √KWAY(AM) (VT48/12).