Son of Eöl whose treachery led to the fall of Gondolin, translated “Sharp Glance” (S/133). His name is a combination of maeg “sharp” and glîn(n) “gleam, glint” (SA/maeg, glîn; WJ/337).
Conceptual Development: In the earliest Lost Tales, his name was G. Meglin (LT2/164), and remained N. Meglin in Silmarillion drafts from the 1930s (SM/136, LR/274). The meaning of the earliest form of this name is unclear, but N. meglin appears in The Etymologies as an adjectival form of megli, so perhaps it was intended to mean “✱bear-like”. In Silmarillion revisions from the 1950s-60s, Tolkien considered several other replacements: Glindûr, Targlîn, Morlîn and Morleg (WJ/91, 323), but ultimately settled on Maeglin (WJ/122, note §119).
maeg (“sharp, piercing, penetrating”) + glîn (“gleam, glint [of eyes]”)