The forest between the rivers Sirion and Gelion, translated “Forest between the Rivers” (S/123), a combination of taur “forest”, im “between” and the class-plural of duin “river” (RC/625).
Sindarin
Taur-im-Duinath
noun. forest between rivers
taur-im-duinath
place name. Forest between the Rivers
Elements
Word Gloss taur “forest, wood, forest, wood, [N.] great wood, [G.] dense wood” im “between” duin “(large) river, (large) river; [N.] water”
taur (“great wood, forest”) + im (prefix “between”) + duin (“long and large river”) + ath (collective plural suffix)