A root in linguistic notes from 1959 used for the sense “hard, difficult” in Sindarin because other roots like √GUR > S. gor- gained a very negative sense due to collision with the roots √ÑGOR “horror” and √ÑGUR “death” (PE17/154). Tolkien first gave this root as √DIR before switching it to √DER. There is no indication of its use in Quenya, so it is probably a Sindarin-only innovation.
Primitive elvish
ur
root. heat, be hot
ūr
noun. a fire (on hearth)
der
root. hard, difficult
nar
root. fire, fire, [ᴹ√] flame
A root for “fire” first appearing as ᴹ√NAR “flame, fire” in The Etymologies of the 1930s along with derivatives like ᴹQ. nár(e)/N. naur “flame” (Ety/NAR¹). There was also an augmented variant ᴹ√ANÁR that served as the basis for “Sun” words: ᴹQ. Anar and N. Anor (Ety/ANÁR). These roots and the various derivatives continued to appear in Tolkien’s later writings in the 1950s and 60s (PE17/38; Let/425), and in one place Tolkien specified that nār- was “fire as an element” as opposed to √RUYU for an actual blaze.
dērā
adjective. hard, difficult
nāro
noun. fire
srak
root. hard, difficult
This root was connected to “heat” for most of Tolkien’s life. It first appeared as unglossed ᴱ√URU in the Qenya Lexicon of the 1910s, with derivatives like ᴱQ. úrin “(blazing) hot”, ᴱQ. uru “fire”, G. urin “hot, very hot”, and G. urna- “blaze, burn” (QL/98; GL/75). In this early period it was blended with the root ᴱ√UŘU with variant ᴱ√USU which had derivatives like ᴱQ. urna “oven” and ᴱQ. usta- “burn” (QL/98). This second root had derivatives in the contemporaneous Gnomish Lexicon such as G. gund “boil, pus” and gusta- “burn, destroy” from primitive ✱gudh (GL/42), indicating the actual root form was ✱ᴱ√ƷUÐU.
✱ᴱ√ƷUÐU seems to have been abandoned in Tolkien’s later writings, but ᴹ√UR “be hot” appeared in The Etymologies of the 1930s with derivatives like ᴹQ. úr/N. ûr “fire” and ᴹQ. urya- “blaze” (Ety/UR). This entry was deleted and replaced by ᴹ√UR “wide, large, great”. This was likely a transient change, however, as ᴹQ. Úrin as a name of the Sun remained in contemporaneous Silmarillion drafts (LR/240). Indeed primitive √UR appeared several times in later writings as the basis for words for “sunlight”, “fire” and “heat” (PE17/120, 148; PE21/71; PE22/160).