The great chain that bound Melkor after his defeat by the Valar (S/252).
Conceptual Development: This name had a long history in Tolkien’s legendarium, appearing in the earliest Lost Tales in various forms, most commonly ᴱQ. Angaino (LT1/103). In the Qenya Lexicon from the 1910s, it was glossed “Tormentor” and given as a derivative of the root ᴱ√ŊAHYA “hurt, grieve” (QL/34). The form Engainor >> ᴹQ. Angainor emerged in The Lays of Beleriand (LB/205, 208) and remained the same thereafter.
Possible Etymology: The later meaning of this name is unclear. Christopher Tolkien connected it with Q. anga “iron” in The Silmarillion appendix (SA/anga). However, the earlier name ᴱQ. Angaino was glossed “Oppressor” or “Tormentor”, and J.R.R. Tolkien was quite emphatic that it was not etymologically related to “iron” (GL/37, G. Gainu). He derived it instead from the root ᴱ√ŊAHYA (or NAẎA) “hurt, grieve” (QL/34).
This early root survived into Tolkien’s later writings as √NAY “cause pain, lament” (Ety/NAY, PE17/166). An intriguing possibility is that the older etymology of Angainor and its resulting glosses could have remained valid as well. The initial element of Angainor might have developed from a strengthened etymological variant of this root, perhaps √NAY > √ÑAY > ✶ṇ̃gay- > Q. Angai-.
As enticing as this idea is, it does not fit the phonology of later Quenya very well. A syllabic initial nasal ✶ṇ̃g- ordinarily developed into Q. ing- (PE19/77), such as ✶ñgōlē > ingolë “lore, science” (PM/360). Furthermore, N/Ñ is not a standard etymological-variation, since these variations did not usually cross homorganic grades (PE18/90). There is no evidence that Tolkien considered such a scenario in any of his later writings.