Fourth son of Finarfin (S/61), variously translated “Fell Fire” and “Sharp Flame”. His name is an adaption of his Quenya mother name Aicanáro (PM/346). This name seems to be a compound of aeg “point” and the suffixal form -nor of naur “fire” (SA/nár).
Possible Etymology: His Quenya name was translated “Fell Fire”, from the element Q. aica “fell”, but Tolkien said that Aegnor was not a true Sindarin name, since there was no Sindarin word ✱✱aeg meaning “fell” (PM/347). Rather, a true translation of his name would be Goenor (PM/363).
There is, however, a Sindarin word aeg meaning “point; sharp, pointed, piercing”, attested in the name Aeglos “Snow-point” and in the word aeglir “range of mountain peaks” as in Hithaeglir “Misty Mountains”. Thus “Sharp Flame” might be a false etymology for this name. This alternate translation appeared in the Silmarillion Appendix (SA/nár) and some early writings from the 1950s (MR/323), but it may be that this was simply an earlier, rejected translation rather then a false etymology.
Conceptual Development: In Silmarillion drafts from the 1930s, his name was N. Egnor (SM/15, 88; LR/116, 223), and at this stage the initial element of his name was N. êg “thorn” from the root ᴹ√EK “spear” (Ety/EK, NAR¹). In draft notes associated with the “Shibboleth of Fëanor”, Tolkien considered changing this name to S. Eignor (VT41/19 note #19), but this seems to have been a transient idea.
fell fire; aeg (from Q aika “fell”) + naur (“flame”) S form of Q Aikanáro “sharp flame, fell fire”; the name was not true S, as there was no S adjective corresponding to Q “fell, terrible”, though aeg would have been its form if it had occurred.