A noun in The Etymologies of the 1930s glossed “frost” derived from the root ᴹ√KHEL “freeze”, but Tolkien deleted this short root and its derivatives, keeping only the longer form ᴹ√KHELEK (Ety/KHEL).
Conceptual Development: The Gnomish Lexicon of the 1910s had a number of similar “frost” related words: G. heloth “frost”, G. hîl {“ice-cold, icy” >>} “frost” as well as G. helfileg “frost on panes, etc.” (GL/48-49), all based on the early root ᴱ√HELE “freeze”, the last with the added element G. fileg “fern”.
Neo-Sindarin: Tolkien probably deleted N. hell “frost” because he abandoned the short root ᴹ√KHEL, but short √KHEL did reappear in later writings (PE17/116), so it is tempting to restore hell “frost” as well. However, this conflicts with other attested words like N. hell “naked”, so I think it is better to use a neologism like ᴺS. nich for “frost”; see that entry for discussion.
A noun in The Etymologies of the 1930s glossed “ice” derived from the root ᴹ√KHELEK of the same meaning (Ety/KHELEK).
Conceptual Development: G. heleg “ice” also appeared in the Gnomish Lexicon of the 1910s along with a variant helc, both under primitive χele-k (GL/48). This is clearly related to the early root ᴱ√HELE as first suggested by Christopher Tolkien (LT1A/Helkar; QL/39).