Final answer:
The word that best fits the definition 'ruled the Byzantine Empire with her husband' is Theodora, who was the wife of Emperor Justinian I and co-ruled the Byzantine Empire.
Step-by-step explanation:
The word that best fits the definition "ruled the Byzantine Empire with her husband" is Theodora. She was the empress and wife of Emperor Justinian I, who ruled from 527 to 565 AD. Theodora was known for her powerful influence and was considered one of the most important empresses of the Byzantine Empire. Despite her low birth and controversial past as an actress and possibly a courtesan, Theodora achieved almost a co-equal share in ruling the empire alongside Justinian. Her presence is notably seen in art, such as the mosaic panel devoted to her in the Basilica of San Vitale.