The name of tengwa #36 [.] in The Lord of the Rings Appendix E (LotR/1123), a derivative of √UR “heat” (PE22/160). This name probably reflects its use for u-diphthongs in Tengwar spelling.
Conceptual Development: In the 1st edition of The Lord of the Rings the name of tengwa #36 was úr “heat” (RC/736), and in earlier documents on The Feanorian Alphabet this word was glossed “fire, heat” (PE22/51) or just “fire” (PE22/23); see the discussion under ᴹQ. úr for further details.
úr noun "fire" (UR)This stem was struck out in Etym, but a word that must be derived from it occurs in LotR, so it seems that Tolkien restored it. Early "Qenya" also has Ûr, noun "the Sun" (also Úri, Úrinci ("k"), Urwen) (LT1:271). Cf. Úri.