The root √KHEP appeared with gloss “retain, keep, do not give away or release, keep hold of” in etymological notes from 1959-60 along with a variant √KHAP “bind, make fast, restrain, deprive of liberty” (VT41/6), and in this period it was almost certainly the basis for S. heb- “keep” in ú-chebin estel anim “I have kept (heb- lenited 1st-person) no hope for myself” (LotR/1061). It might be a later iteration of ᴱ√HEPE, glossed “bind” in the Qenya Lexicon of the 1910s (QL/40) and “encircle?” (the question mark is Tolkien’s) in the contemporaneous Gnomish Lexicon (GL/48).
Neo-Eldarin: For purposes of Neo-Eldarin, some derivatives of this 1910s root might be salvaged as derivatives of later √KHEP.
This root was the basis for “ice” words all the way back in the Qenya Lexicon of the 1910s, where ᴱ√HELE appeared with variant ᴱ√HḶKḶ as the basis for words like ᴱQ. helke “ice”, ᴱQ. helka “ice-cold”, ᴱQ. halkin “frozen”, and ᴱQ. hilk- “freeze” (QL/39). The root was given as {hele-k >>} χele-k in the contemporaneous Gnomish Lexicon with derivatives like G. hel- “freeze”, G. heleg “ice” and G. helc “ice-cold, icy, cold” (GL/48). The Gnomish forms do not show the kinds of vowel-variations that would indicate the presence of ancient syllabic Ḷ, so perhaps Tolkien had abandoned ᴱ√HḶKḶ by that point.
The root reappeared in The Etymologies of the 1930s as ᴹ√KHEL “freeze” and extended root ᴹ√KHELEK “ice”, with the reappearance of many derived forms as well such as ᴹQ. helke/N. heleg “ice” and ᴹQ. helka/N. helch “ice-cold” (Ety/KHEL). Tolkien’s continued use of words like Q. Helcaraxë “Grinding Ice” indicate the ongoing validity of the extended root √KHELEK (S/134), and the shorter root √KHEL “ice” appeared in later notes of the origin of S. Forochel (PE17/116).