Complex sentence: Called in English "Grey-elvish" or "Grey-elven", it was the primary language of the Sindar Elves of Beleriand, Elves of the Third Clan or Teleri who remained behind in Beleriand after the Great Journey.
Split into simpler sentences: Called in English "Grey-elvish" or "Grey-elven", it was the primary language of the Sindar Elves of Beleriand. These were Elves of the Third Clan, often called Teleri, who remained behind in Beleriand after the Great Journey.