Why did Dionysus change his mother's name?

Question

Semele was the mortal mother of Zeus' son Dionysus. She was tricked by the jealous Hera and she ends up dying.

Dionysus survived, but when he grew older, he was concerned for his mother and retrieved her from the Underworld:

Dionysus feared for his mother, whom he had not seen since birth. He bypassed the god of death, known as Thanatos, thus successfully returning Semele to Mount Olympus. Out of the twelve Olympians, he was of the few that could restore the deceased from the underworld back to life. ^[1]

However, once Semele was among the gods, Dionysus refers to her under the name Thyone:

THYO′NE (Thuônê), the name of Semele, under which Dionysus fetched her from Hades, and introduced her among the immortals.^[2]

Was there a specific reason for this name change?

Answer 1

When Dionysus fetches Semele from Hades and introduces her to Olympus, she is no longer a human being, but a goddess. The name change is actually due to this transformation.

Στην ελληνική μυθολογία το όνομα Θυώνη ήταν μια άλλη ονομασία της μητέρας του θεού Διονύσου, της Σεμέλης. Η εξήγηση που δίνεται για τη μεταξύ τους διαφορά είναι ότι «Σεμέλη» είναι η θνητή υπόσταση της μητέρας του θεού, ενώ «Θυώνη» είναι η Σεμέλη μετά την αποθέωσή της (δηλαδή τη μετατροπή της σε θεά) από τον Διόνυσο, ο οποίος την έφερε στον Όλυμπο παίρνοντάς την από τον Άδη.

_{source: Wikipedia article on Thyone}

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In Greek mythology the name Thyone was another name of Dionysus' mother, Semele. The difference is that Semele is a mortal aspect of Dionysus' mother, while Thyone is actually Semele after her Αποθέωσις (which means deification in Greek).

Little is however known about the etymology of the name Semele. One theory is that it's derived from the word Θεμέλη which means Earth in ancient Greek. That said, the names are tied to Themele's subsistence at the time.