G-form

Form I is the base, or ground, form of the verb and will be referred to henceforth as the "G-form," the Semitic designation, from Grundstamm (“base stem”)

Koranic Arabic verbs don't occur only with -a-a- vowels — like kataba ‘he wrote’ — in the Pf-stems of their active G-forms: some transitive action verbs like šariba ‘drink’ and several stative and psychological verbs like ḥasiba ‘suppose’ have i as their second stem vowel, [...]