The root ᴹ√BOR “endure” along with its extended form ᴹ√BORON appeared in The Etymologies of the 1930s along with various derivatives having to do with endurance, faithfulness and everlastingness (Ety/BOR, BORÓN). It was simply a later version of the root ᴱ√VORO from the Qenya Lexicon of the 1910s, unglossed but clearly of a similar meaning based on its Qenya and Gnomish derivatives like ᴱQ. voronda “faithful”, ᴱQ. vorima “everlasting” and G. bron(n) “steadfast, firm” (QL/102; GL/23-24).
Similar forms like Q. voronda or vórima “faithful” continued to appear in Tolkien’s later writing (UT/317). The well established names Q. Voronwë or S. Bronwe(g) “Steadfast, Faithful” retained the same basic form and meaning throughout Tolkien’s life, testifying to the enduring nature of the Elvish root for “endurance”.
A root in The Etymologies of the 1930s glossed “day” with various derivatives like ᴹQ. are, N. aur “day” and ᴹQ. arin “morning” (Ety/AR¹). In Tolkien’s later writings, the Quenya word for “day” became aurë (RC/727; S/190), and in 1957 Quenya Notes he devised a new etymology for these day-words from the root √UR “heat” as in ✶auri “heat, period of sun” (PE17/148). That opens the question whether the various 1930s Quenya “morning” words from ᴹ√AR remain valid, but many Neo-Quenya writers (including me) retain them since there aren’t really any good alternatives. They might be salvageable as derivatives of the later root √AS “warmth” (so that “day” = “hot” and “morning” = “warm”).