A Doriathrin noun for “tree” derived from the root ᴹ√GÁLAD (Ety/GALAD), probably from a primitive form ✶galadā with the second a* lost due to the Ilkorin Syncope. Note that the first element [[ilk|[gal-] did not reduce to [gl-]]] because the initial syllable was stressed in the primitive word.
A Doriathrin noun for “tree” derived from the root ᴹ√ÓR-NI or ᴹ√ÓRON (Ety/ÓR-NI, EtyAC/NEL). According Tolkien, it was “in Doriath used especially of beech, but as a suffix [it was] used of any tree of any size” (Ety/ÓR-NI). The root ᴹ√ÓR-NI in The Etymologies suggests a primitive form of ᴹ✶ornĭ, but elsewhere Tolkien indicated the primitive form was ᴹ✶ornē (e.g. on SD/302). Both primitive forms would have produced Ilk. orn, as noted by Helge Fauskanger (AL-Doriathrin/orn).