In ancient Greek weddings, the bride and bridegroom were attended by paranymphs and, from this use, it has been generalized to refer to attendants of doctoral students, best men and bridesmaids in weddings and the like.
[1] It can refer specifically to the friend of a bridegroom tasked with accompanying him in a chariot to fetch the bride home.
An obscure use of the word is as a spokesman for the bride or bridegroom, such as Cyrano de Bergerac towards Roxanne.
[2] This ritual originates from the ancient concept where obtaining a doctorate was seen as a de facto marriage to the university.
Today the role is symbolic and seen as a position of honour similar to a best man or woman at a wedding.