Nice scholarly paper on Tolkein’s writings describing elf-sex:
There was at least one elvish word related to a sexual act in Quenya or Sindarin: nosta / onna, beget. The source for this is Treebeard’s farewell to Galadriel and Celeborn in “Many Partings,” ROTK. This farewell includes the Quenya phrase “O vanimar, vanimalion nostari”, translated in The End of the Third Age, in the chapter discussing Many Partings, footnote 16, as “fair ones begetters of fair ones.” There is a related early Quenya noun, ontâro, meaning begetter/masculine parent. The early Quenya word wegê, meaning manhood or vigor, may be open to a variety of interpretations. There was also a Quenya word meaning virgin, rod, as in Rodwen, “High Virgin Noble (female).” (Maeglin, The War of the Jewels, HME)
(via MeFi)