pactum

Pactum is a Latin noun meaning an agreement or contract. In English, the term survives mainly in legal and historical contexts, and it is the etymological source of the modern word pact. The plural form is pacta.

In Roman law, pactum referred to a binding agreement that created obligations between the parties. Over time, pacta sunt servanda—“agreements must be kept”—became a foundational principle indicating that contracts should be honored. In modern civil and international law, the concept remains fundamental: agreements, whether private contracts or treaties, are intended to be enforceable and performed in good faith.

The term appears in various specialized forms, such as pacta de non petendo (agreements not to sue) and other private arrangements. In international law, treaties are commonly described as pacts or covenants, and states are bound to fulfill them under the principle of pacta sunt servanda.

In contemporary English usage, pactum is encountered mainly in legal writing or historical discussion; everyday language typically uses contract or agreement. The word also informs English and Romance-language terms such as pact, pacte, and covenant, reflecting its historical role in shaping the concept of binding arrangements between parties.