Consubstantial (Latin: consubstantialis) is an adjective used in Latin Christian christology, coined by Tertullian in Against Hermogenes 44, used to translate the Greek term homoousios. "Consubstantial" describes the relationship among the Divine persons of the Christian Trinity and connotes that God the Father, God the Son, and God the Holy Spirit are "of one being" in that the Son is "generated" ("born" or "begotten") "before all ages" or "eternally" of the Father's own being, from which the Spirit also eternally "proceeds."

Since the Latin language lacks a present active participle for the verb "to be," Tertullian and other Latin authors rendered the Greek noun "ousia"(being) as "substantia," and the Greek adjective "homoousios" (of the same being) as "consubstantialis". Unlike the Greek words, which are etymologically related to the Greek verb "to be" and connote one's own personal inherent character, "substantia," connotes matter as much as it connotes being.

The term is also used to describe the common humanity which is shared by all human persons. Thus, Jesus Christ is said to be consubstantial with the Father in his divinity and consubstantial with "us" in his humanity. This term was canonized by the Orthodox Church in 325 at the council of Nicaea.