There are numerous examples in the Etymology where a final [l], [r], [n], [m] became syllabic after another consonant and developed an intervening vowel. This vowel was [o] in most cases, but was [u] in the case of final [m]: ᴹ✶khithme > Dor. hidhum (EtyAC/KHIS).

It seems this change did not occur for certain favored combinations, where which retained. There are several examples in which final [-rn] did not develop a vowel, such as Dor. dorn or Ilk. arn (Ety/DÓRON, YAR). There is one case in which final [-lm] did not develop a vowel: Ilk. lalm (Ety/ÁLAM), but another where it did: Ilk. talum (Ety/TAL). The two examples are very similar, so they may represent some uncertainly on Tolkien’s part on the development of final [-lm] in Ilkorin.