biface

Historically, "biface" comes from lithic archaeology, where it names flint, chert, obsidian, and other stone tools that have been intentionally worked on both sides—often called bifacial tools. The most familiar example is the symmetrical hand-axe, but the category also includes knife-like forms, projectile preforms, and many regional variants. Ancient knappers used this two-sided method to improve edge control and durability, so one piece of stone could carry both symmetry and utility.

In everyday speech, "biface" is less common than its adjective form, "bifacial," and it is not a standard dictionary way to describe a person who behaves differently in different situations. The closest common sense is "two-faced," though that is usually a separate term with a moral judgment attached. So if you use "biface," it usually stays closer to archaeology and material culture than to character description.