Sindarin 

ereth

noun. solitude, oneness, loneliness

Cognates

  • Q. eressë “solitude, [ᴹQ.] solitude; [ᴱQ.] alone, by oneself, singly, only; once”

Derivations

  • ER “one, single, alone, one, single, alone; [ᴹ√] be alone, deprived; [ᴱ√] remain alone”