Aquinas reintroduced the theological term inimicus into just war theory.

Evidence

It is in his famous discussion of war that Aquinas invokes the term that, recalling Jesus’ commandment, has otherwise tended to vanish from discussions of war, and of just war in particular: inimicus. — Gil Anidjar, The Jew, the Arab, 196

Categorization

• DEFINE: Distinguishes inimicus (personal/neighbor enemy) from hostis (military enemy) as distinct Latin terms for enmity.