The Quenya term for those with mixed Mannish and Elvish blood such as Elrond and Elros (Let/386, PM/348), though in The Lord of the Rings itself, only its Sindarin equivalent Peredhil was used (LotR/1034). Pereldar is a compound of the prefix per- “half-” and the plural of Elda “Elf”.
Conceptual Development: The term ᴹQ. Pereldar appeared in The Etymologies, but there it was translated “Half-eldar” and referred to those Elves such as the Danians who turned back on the journey to Valinor (Ety/PER, LR/215). Pereldar was first applied to the Half-elves in the draft of The Lord of the Rings (RS/412). In later writings, the term for the Elves who did not go to Aman was Q. Úmanyar.
Pereldar pl. noun "Half-elven" (= Sindarin Peredhil) (Letters:282), in the Etymologies used of the Danas or Nandor (PER). Sg. #Perelda.