The Quenya name of S. Elros (PM/349), a compound of elen “star” and rossë “dew”. The final -n of elen was assimilated to the r, which also happened in the names Elerondo and Elerrína.
Quenya
Elerossë
star foam
elerossë
masculine name. Star Foam
Elerondo
star-vault
*Elerondo masc_. _name "Star-vault", Sindarin Elrond. Extrapolated from Elerondiel "daughter of Elrond", patronym of Arwen (PE17:56); cf. Elerossë, rondo.
Elerossë masc. name, "star foam", starlit foam, Sindarin Elros(PM:348)