An adjective in The Etymologies of the 1930s glossed “mighty, vast, overwhelming, huge, awful” derived from primitive ᴹ✶taurā “masterful, mighty” based on the root ᴹ√TUR “power, control, mastery, victory” (Ety/TÁWAR, TUR). It was also influenced by ᴹ✶tārā “lofty” and as such had the alternate meaning “high, sublime”. Thus its gloss “awful” has the sense “causing awe” rather than its modern English meaning “terrible”, and its general meaning seems to something that is mighty (in strength or size) and also induces awe, either inspiring or terrifying. Its Quenya equivalent Q. taura continued to appear in later writings (PE17/115, VT39/10), indicating that this Noldorin word probably remained valid in Sindarin.
Conceptual Development: The Gnomish Lexicon of the 1910s had the adjective G. taura “powerful” and the (archaic) noun G. †taur “ability, power” (GL/69), both based on the early root ᴱ√TURU “am strong” (GL/72; QL/95).
An (archaic) word for “brother” in The Etymologies of the 1930s derived from the root ᴹ√TOR of the same meaning, with an irregular plural terein (Ety/TOR). In ordinary speech, it was replaced by muindor, with an initial element muin “dear”.
Neo-Sindarin: In notes from the late 1960s, Tolkien introduced a new word hanar for “brother” (VT47/14). However, I think †tôr and related words might be retained to mean a “metaphorical brother”, a close male associate who may or may not be related by blood, as with such words as gwador “(sworn) brother, associate”. In this paradigm, I would assume muindor still refers to a brother by blood, with an added connotation of strong affection.