This Primitive Adûnaic phoneme is a weak voiced velar continuant described as “the ‘clear beginning’ or possibly the ‘glottal stop’”: IPA [ʔ] (SD/432). It appears only in ancient writing and disappeared early without any apparent effects (SD/419), so from the perspective of later Adûnaic, it may as well have not existed at all.

Tolkien represented this sound by the symbol “?” in the typescript of Lowdham’s Report. Since this could be confused with a mark of uncertainty, the discussion here uses the IPA symbol “ʔ” to represent the sound orthographically as well as phonetically, though the only attested root in which this sound appears is ʔIR (SD/432).