Basi- \Ba"si-\ A combining form, especially in anatomical and botanical words, to indicate the base or position at or near a base; forming a base; as, basibranchials, the most ventral of the cartilages or bones of the branchial arches; basicranial, situated at the base of the cranium; basifacial, basitemporal, etc.

Source: Webster's Revised Unabridged Dictionary (1913)