A Christian heresy of the 5th and 6th centuries that challenged the orthodox definition of the two natures (human and divine) in Jesus and instead believed there was a single divine nature WordNet 3.0 & Open English WordNet

Monophysitism or monophysism is a Christology that states that in the person of the incarnated Word there was only one nature—the divine. Wikipedia

Christological term and doctrine which emphasizes the one holy, divine aspect and nature of Christ Wikidata

A Christian belief which holds that the human nature of Jesus Christ was essentially absorbed by the divine, and thus that he essentially had but one nature, contrary to the orthodox view that Christ has two natures, both fully human and fully divine. A variant is apollonarianism, which has gnostic overtones and used hellenistic ideas alien to orthodox Christianity. Wiktionary

Christian believe claiming a human-only nature of Jesus Christ. Wiktionary (translation)