In the initial syllable of a polysyllabic word, unstressed vowels tended to vanish if the result was one of several favored consonant combinations: br-, dr-, gr- or tr-. This change also occurred with mr-, but then the initial [mr-] became [br-]: ᴹ✶morókō > Ilk. broga (Ety/MORÓK). Finally, the change could occur when the favored initial combination was preceded by another consonant, such as: ᴹ✶MBIRÍL > Ilk. (m)bril (Ety/MBIRIL) or ᴹ✶starāna > [strāna >] Ilk. thrôn (Ety/STARAN).

In the examples of this change, the words in question had either stress marker or a long vowel in the second syllable, indicating that the first syllable was unstressed (see below). Furthermore, there are some counter-examples where the first syllable is marked as stressed and the vowel loss does not occur: ᴹ✶bóron- > Ilk. boron (Ety/BOR), ᴹ✶DÓRON > Ilk. dorn (Ety/DÓRON). Finally, in all the attested examples, the lost vowel is followed by another of the same quality.

It is possible that this change occurred with other initial combinations such as pr- or kr- that are simply missing in the small list of available Ilkorin words. It is also possible that this change occurred in Common Eldarin rather than Ilkorin, since these combinations are listed as Later Combinations in the Comparative Tables (PE19/21). These tables also list combinations involving [l], such as bl- or gl-, but there are no such attested examples in Ilkorin. It is unclear whether this is because such changes did not occur, or because such examples are simply missing from the available Ilkorin word list.