This Primitive Adûnaic phoneme was a nasal in the k-series (velars), described as “the sound of ‘ng’ in English ‘sing’” (SD/417). Very probably it was the velar nasal, pronounced as the “n” in English “sing” or “sink”. It did not exist as an independent word-forming element: it could only appear from nasal-infixion before velars and by assimilation of the dental nasal [n] to a following velar consonant (SD/420, 432).

In English, [ŋ] is an allophone with [n], and the two sounds may have been allophones in Primitive Adûnaic as well. However, the two sounds were not allophones in either Primitive Elvish or classical Quenya, both of which heavily influenced Adûnaic. When the Númenóreans first adopted Elvish writing, they might have used both letters for these sounds, tengwa #17 (númen) for [n] and tengwa #19 (ñoldo) for [ŋ], or they could have used tengwa #17 for both.

As noted above ✶[ŋ] could only appear before another velar. The only combination that survived into Classical Adûnaic was [ŋg] (SD/433 note #5). Before ✶[k] or [kʰ], ✶[ŋ] became [k] (SD/420). Before ✶[x], ✶[ŋ] became [x] (SD/420), producing the double-spirant [xx] (“kkh”). Both ✶[ŋg] and ✶[ŋɣ] become [ŋg] (SD/421-2).

Tolkien represented this sound with the symbol “9” in the typescript of Lowdham’s Report, but elsewhere he usually used the symbol “ñ” for this sound. He probably only used a “9” because he was working on a typewriter. The discussion of Adûnaic here uses the symbol “ñ” to represent [ŋ] orthographically.