A noun in The Etymologies of the 1930s glossed “brother” that was “especially used of those not brothers by blood, but sworn brothers or associates”, a combination of prefix N. gwa- “together” with the root ᴹ√TOR “brother” (Ety/TOR).
Quenya
otorno
brother, sworn brother, [male] associate
otorno noun "brother, sworn brother, [male] associate" (TOR, WŌ). Cf. osellë.