The unglossed root ᴹ√THON appeared in The Etymologies of the 1930s with derivatives Ilk. thōn and N. thaun “pine-tree” (Ety/THOL); according to Hostetter and Wynne, Christopher Tolkien incorrectly recorded this root as ᴹ√THŌN, but that was actually just the Ilkorin form of the word. Tolkien explained the somewhat unusual Noldorin form N. thaun as the result of a loan for Ilk thōn, with the Noldorin word being adapted as ō [ǭ] < [primitive] ā; this loan must have occurred in the period after ancient long [ō] became [ū] in Old Noldorin, but before [ǭ] (from [ā]) became [au]. This 1930s root was used mainly to explain the name Ilk. Dorthonion “Land of Pines”.

In a 1955 letter to David Masson, Tolkien derived S. thôn “pine” from ✶stŏna (PE17/82). However, in Words, Phrases and Passages from the Lord of the Rings written in the late 1950s or early 1960s Tolkien derived this element of S. Dorthonion from {stāna >> thānĭ >>} thŏno, apparently coming full circle back to the 1930s root √THON (PE17/81).