The great mariner who took the Silmaril of Beren to Valinórë, thereby instigating the Valar’s liberation of Beleriand and the final defeat of Morgoth (S/246). His name was a compound of ëar “sea” and the suffix -(n)dil “-friend, -lover” (SA/ëar, (n)dil).
Conceptual Development: This was one of the oldest and most important names in Tolkien’s legendarium. Tolkien admitted that the name was inspired by the Anglo-Saxon word éarendel “ray of light” (Let/150, 385). In fact, the first form of this name in the Lost Tales was ᴱQ. Earendel (LT1/13), often spelt Earendl in Tolkien’s early linguistic notes (QL/34, PE13/99). At this stage the name seems to derive from ᴱQ. earen (earend-) “eagle, eyrie” (QL/34), though the “dialectical form” Yarendl was archaically used for “mariner” (QL/105).
The name remained ᴹQ. Earendel in Silmarillion drafts from the 1930s (LR/326) and up through Lord of the Rings drafts from the 1940s (RS/215, TI/99, WR/223 note #29). The name’s association with the Sea did not emerge until Tolkien wrote the (unfinished) “Notion Club Papers” story in the mid-1940s, at which point its form changed to ᴹQ. Earendil (SM/237, 241) and so remained thereafter.
Eärendil, masc. name; see ëar. Eärendilyon noun "son of Eärendel" ("used of any mariner") (LT1:251)