Sobriquet of Beren after his hand was bitten off during his quest for a Silmaril (S/183). The two initial elements of this name are er “one” and a mutated form cham of cam “hand” (SA/er, cam). The second of these is especially interesting, in that it is a rare example of liquid-mutation. The meaning of the final element is unclear, but it is probably a variant of the masculine suffix -on. As further evidence of this, Tolkien also wrote Erchamon without the i, and according to Patrick Wynne this was clearly deliberate and not a slip (VT47/7, PE21/86).
Conceptual Development: In the earliest Lost Tales from the 1910s, this name appeared as G. Ermabwed (LT2/34). In Silmarillion drafts from the 1930s, this name was revised first to (Ilkorin?) Ermabuin (SM/310), then again to N. Erchamui (LR/146, LR/405). In one place it appeared as Erchamron (Ety/MAP).
As a variation on all these names, the forms N. Er(h)amion or Erchamion appeared as early as the Lays of Beleriand from the 1920s (LB/119, 121) and also in Silmarillion drafts from the 1930s (LR/146, 405). In Lord of the Rings drafts from the 1940s, this name appeared as Erhamion (RS/183) and was firmly established in its final form Erchamion by the time of the Silmarillion revisions from the 1950s-60s (WJ/51, 231).