A forested region in northern Beleriand, meaning “Land of Pines”. After its corruption by the forces of Morgoth, the region was renamed to Taur-nu-Fuin.

Possibly Etymology: The name contains the elements S. dôr “land” and thôn “pine”, but its final element -ion is harder to explain. It could be the suffix -ion² “-land” appearing in names like Eregion and Rhovanion, but then both the first and final elements of Dorthonion would mean “land”, which seems unlikely.

In one note (PE17/81), Tolkien said that this word was “Sindarin Noldorized”, so perhaps the final element is the Quenya genitive plural -ion, so that -thonion is Quenyarized Sindarin for “of Pines”. In the same note, Tolkien gives Dor i Thuin, apparently as the proper Sindarin name of the region. Since Dorthonion is where many Noldor settled after their arrival in Beleriand, this scenario is plausible.

Conceptual Development: In Silmarillion drafts from the early 1930s, this name first appeared as Taur Danin (SM/107), later revised to Taur-na-Danion “Forest of Pines” (SM/296, LR/145) with variants -Thanion, -Donion, -Thonion. It became Dorthanion >> Dorthonion in Silmarillion drafts from the mid-1930s (LR/145, 257), the last of these forms being used thereafter.

In The Etymologies, Tolkien specified that the name was from the Ilkorin language, Ilk. Dorthonion “Land of Pines”, while its Noldorin form was N. Dor-na-Thuin (Ety/THŌN). Since the Ilkorin language also used -(i)on for is genitive plural, this is an earlier parallel of the Quenyarized Dorthonion versus proper Sindarin Dor i Thuin discussed above.

Earliest name of Dorthonion in Silmarillion drafts from the 1930s, first appearing as Taur Danin (SM/197) and later expanded to Taur-na-Danion (LR/127) with variants -Thanion, -Donion, -Thonion before ultimately being replaced by the Ilkorin name Dorthonion (LR/145). It is a combination of taur¹ “forest”, na “of” and early variants of thaun “pine”, possibly as an earlier Gnomish-style genitive plural.

See S. Dorthonion for further discussion.