Tolkien never specifically discussed single-vowel Primitive Adûnaic words, but there are numerous examples of words from biconsonantal-roots that have only a single characteristic vowel. This vowel is always in the normal position between the first and second consonant. For example, the primitive word ✶khaw “crow” fits this pattern, and classical Adûnaic words like bêth “word”, bâr “lord”, nûph “fool” and pûh “breath” were most likely derived from single vowel biconsonantal primitive forms, from the roots ✶Ad. √BITH, *√BAR, *√NUPH and *√PUH.

The case for single-vowel words derived from triconsonantal-roots is more complex. A word like **kal’b from the root ✶Ad. √KALAB is not possible, since clusters are not allowed as the final-consonants of Primitive Adûnaic words. There is, however, one example of a primitive triconsontal word with a single vowel: ✶Ad. √DAWAR > ✶dāw’r > Ad. dâur “gloom”. It seems likely that such primitive single-vowel triconsonantal words were only possible when the semi-vowels [w] or [j] were the middle consonant, since these would develop into vowels when [w] and [j] became [u] and [i] before consonants and finally.