A root appearing in The Etymologies of the 1930s as ᴹ√SKAL “screen, hide (from light), overshadow” (Ety/SKAL¹) with a couple rejected variant meanings “cower, hide” and “conceal, hide (from light)” (EtyAC/SKAL¹, SKAL³). It had derivatives like ᴹQ. halda/N. hall “veiled, hidden, shadowed, shady” and Ilk. esgal “screen, hiding, roof of leaves” as in Ilk. Esgalduin “River under Veil” (Ety/SKAL¹).
The root reappeared as √SKAL “cover, veil, cloak, conceal” with a “privative” √S- prefix added to √KAL “light”, again as the basis for S. esgal “a cast shadow” in S. Esgalduin “River under Shade” (PE17/184). In this note, Tolkien contrasted √SKAL with √SPAN of similar meaning, saying that “√SKAL was applied to more opaque things that cut off light and cast shadows over other things ... √SPAN was applied to things of lighter texture, and corresponds closer to our veil” and also:
> SKAL was primitively verbal [whereas] SPAN was primitively nominal. Thus the most primitive derivative of SKAL was skalā and this meant the action or effect of overshadowing ... But spanā meant a thing that veiled, a veil (PE17/184).
Elsewhere the derivatives of √SPAN were more frequently attributed to √PHAN; see those entries for further discussion.
A root appearing in The Etymologies of the 1930s as ᴹ√SPAN “white” (Ety/SPAN) with derivatives like ᴹQ. fanya/N. fein “white” and ᴹQ. fána/N. faun “cloud”, the latter an element in ᴹQ. Fantur/N. Fannor “Lord of Cloud” as the basis for N. Gurfannor and N. Olfannor which were alternate names of Mandos and Lórien (Ety/SPAN). In writings from the 1910s, these alternate names were instead based on ᴱQ. Fantur/G. Fanthor < ᴱ√FANA; this early root seem to mostly have to do with dreams and visions (QL/37; GL/34).
Starting in the late 1950s, Tolkien began using √FAN or √PHAN “white” as the basis for cloud words (PE17/26, 36). √SPAN “cover, veil, cloak, conceal” was restored in a 1967 discussion of the root √SKAL of similar meaning where Tolkien said “√SKAL was applied to more opaque things that cut off light and cast shadows over other things ... √SPAN was applied to things of lighter texture, and corresponds closer to our veil” and “SKAL was primitively verbal [whereas] SPAN was primitively nominal” (PE17/184). However, towards the end of this note Tolkien wrote “Keep this part so far as it affects SKAL”, hinting that √SPAN was discarded; this rejection may have been tied to his introduction of a privative sense to prefixal √S- which worked for √S-KAL (“without light”) but not √SPAN. He wrote several other lengthy essays in 1967 with √PHAN = “veil”; see that entry for discussion.