The Nuffic Glossary is a list with explanations of terms used in Dutch education.
This Dutch term refers to the ceremonial assistant of the doctoral candidate at the PhD defence ceremony. As the van Dale dictionary describes: "a person who accompanies and assists someone who presents his/her thesis". There is no direct equivalent in English; any of the above terms may be used, or 'paranymph' with an additional explanation.
Source: van Dale.