Biconsonantal roots had two consonants with a characteric vowel between them, such as ✶Ad. √ZIR “love, desire”. Apparently any of the primitive consonants could appear as either the initial or final consonants. The biconsonantal roots were probably older, with triconsonantal roots developing from them (SD/416), but these developments was far enough in the past that these relationships are difficult to discern. Unlike the Elvish languages, verb forms were usually triconsonantal roots, though a few common verbs were derived from biconsonantal forms (SD/416).

With vowel-variations, words derived from biconsonantal bases could take the form ✶zir(i), ✶izri (SD/418) or ✶izir (SD/422). In the first pattern, the second vowel can be omitted or it could be different from the characteristic-vowel (SD/423): ✶zir, ✶zira, ✶ziru. In the second and third patterns, both vowels are required and must match the characteristic vowel (SD/434). From these three basic patterns, the root could undergo further root-modifications.