Any of the Primitive Adûnaic consonants could appear initially, with the exception of [ŋ], which only appeared in the middle of words before other velars (SD/432). Primitive Adûnaic words began with at most a single consonant, having no initial consonant clusters (SD/417).

Primitive Elvish words often began with initial-groups of velars [k,kʰ,g,ŋ] + semi-vowels [w,y] (PE18/42, 91). Early Elvish loan words must have changed these clusters to single consonants. The y-groups probably became Primitive Adûnaic palatals (c-series). There is such an example on SD/419, where the Primitive Elvish ᴹ✶kyul(u)mā “mast” likely became ✶Ad. *culum(a) and then Classical Adûnaic sulum.

It is less clear what happened to w-groups, but Ad. bêth “expression, saying, word” is very similar to Sindarin peth “word”, especially in its lenited form beth. The ancient development of this word may have been similar to Sindarin, with Primitive Elvish root √KWET > *√PET > ✶Ad. √BITH, as suggested by Helge Fauskanger (AL/Adûnaic). If so, the (very common) Primitive Elvish ✶kw- may become ✶Ad. b-. From the root ✶Ad. √BITH, the development was almost certainly a-fortification to *baith > bêth.