The Elvish words for “oak” had very similar forms throughout Tolkien’s life. In the Qenya Lexicon of the 1910s, it was ᴱQ. nor(ne) from the root ᴱ√NOŘO, which Tolkien marked with a “?” (QL/67). Its Gnomish cognate G. dorna (GL/30) hints that the true form of this early root might have been ✱ᴱ√NDOÐO or something similar. In the 1930s the root became ᴹ√DORON with derivatives ᴹQ. norno/N. doron “oak” (Ety/DÓRON). This somewhat surprising derivation was explained in the Outline of Phonology from the early 1950s, where Tolkien said:
> n ... also appears occasionally as product of [initial] d, instead of l, by assimilation to succeeding nasals, as in dorno > norno (PE19/80).
In etymological notes from the later 1950s or early 1960s, Tolkien gave the root √DOR “hard, tough”, that in Quenya was preserved only in the word “oak” and in ndŏr > nŏr “land” (PE17/181). Its connection to “oak” indicates this is a later iteration of ᴹ√DORON, though the connection to √NDOR “land” was new. A similar root √DORO “dried up, hard, unyielding” appeared in the contemporaneous Quendi and Eldar essay from around 1959-1960, again connected to √NDOR but without mention of “oak” (WJ/413).
In both sets of notes, √DOR has the Sindarin derivative dorn “tough, stiff, thrawn, obdurate”, also used as another name for the dwarves. However, Tolkien sometimes used norn “Dwarf” instead (PE23/139; WJ/209), reflecting some vacillation on this root.
The Elvish words for “oak” had very similar forms throughout Tolkien’s life. In the Qenya Lexicon of the 1910s, it was ᴱQ. nor(ne) from the root ᴱ√NOŘO, which Tolkien marked with a “?” (QL/67). Its Gnomish cognate G. dorna (GL/30) hints that the true form of this early root might have been ✱ᴱ√NDOÐO or something similar. In the 1930s the root became ᴹ√DORON with derivatives ᴹQ. norno/N. doron “oak” (Ety/DÓRON). This somewhat surprising derivation was explained in the Outline of Phonology from the early 1950s, where Tolkien said:
> n ... also appears occasionally as product of [initial] d, instead of l, by assimilation to succeeding nasals, as in dorno > norno (PE19/80).
In etymological notes from the later 1950s or early 1960s, Tolkien gave the root √DOR “hard, tough”, that in Quenya was preserved only in the word “oak” and in ndŏr > nŏr “land” (PE17/181). Its connection to “oak” indicates this is a later iteration of ᴹ√DORON, though the connection to √NDOR “land” was new. A similar root √DORO “dried up, hard, unyielding” appeared in the contemporaneous Quendi and Eldar essay from around 1959-1960, again connected to √NDOR but without mention of “oak” (WJ/413).
In both sets of notes, √DOR has the Sindarin derivative dorn “tough, stiff, thrawn, obdurate”, also used as another name for the dwarves. However, Tolkien sometimes used norn “Dwarf” instead (PE23/139; WJ/209), reflecting some vacillation on this root.