A root for “brother” that Tolkien introduced in notes on finger-names from the late 1960s as a companion to √NETH “sister” (VT47/14, 26, 34). It conflicts with, and possibly replaces, earlier uses for √KHAN such as √KHAN “back” in notes from around 1959 serving as the basis for the prefix Q. han- in hanquenta “answer” (PE17/166). The root ᴹ√KHAN also appeared in The Etymologies of the 1930s glossed “understand, comprehend”, with various derivatives in both Quenya and Noldorin of similar meaning (Ety/KHAN).
It is unlikely that all these uses of √KHAN coexisted, but I think at a minimum both √KHAN “brother” and ᴹ√KHAN “understand, comprehend” should be retained for the purposes of Neo-Eldarin, as the latter has no good replacements in Tolkien’s later writing. As for hanquenta “answer”, it might be reinterpreted as “a saying providing understanding”, and so be derived from ᴹ√KHAN “understand”.
This root was associated with Elvish words for “birth” for most of Tolkien’s life. It first appeared as ᴱ√NŌ “become, be born” in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. nosta- “give birth to; cause” and ᴱQ. nosse “folk, kin, people” (QL/66). Likewise in the contemporaneous Gnomish Lexicon there was G. nosta- “am born” and G. nothri “family, kinship” (GL/61), and in the Name Lists for to The Fall of Gondolin (NFG), G. nos was used as the equivalent of ᴱQ. nosse (PE15/22, 24). Both Q. nossë and S. nos(s) appeared regularly in Tolkien’s later writings.
In The Etymologies of the 1930s Tolkien gave ᴹ√NŌ/ONO “beget” as an invertible root, with derivatives of the inverted form including ᴹQ. onta- “beget, create” and N. odhron “parent” (Ety/NŌ, ONO). The invertible root appeared regularly in Tolkien’s later writings, usually with the sense “beget” but in one place also glossed “be born” (PE17/170).