A noun for “brother” in The Etymologies of the 1930s derived from the root ᴹ√TOR of the same meaning, with a somewhat irregular plural torni (Ety/TOR). Its stem form is torn-, since with most inflected forms the Quenya syncope comes into play and the second o is lost.
Neo-Quenya: In notes from the late 1960s, Tolkien introduced a new word háno for “brother” (VT47/14). However, I think toron 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 melotorni “love-brother, ✱close male friend” or ᴹQ. otorno “sworn brother”. In this sense, háno would be limited to biological relationships, but toron would refer to brotherly (or brother-like) affection.
A word glossed “brother” under the root ᴹ√NŌ (Ety/NŌ), but in the entry for ᴹ√TOR Tolkien said it was used “usually of the blood-kinship” and its cognate was N. gwanur “kinsman”, which seems like a better translation. It is simply the root ᴹ√NŌ “beget” with the prefix ᴹQ. o- “together” and a masculine suffix.