I've had this stuck in my head for DAYS. Hah. I borrowed the ecplanation for Elphaba's name from the book.
"Hey Elphie?"

The two girls were sitting on the train to the Emerald City, content and quiet. "Hmm?" asked Elphaba, hoping Glinda would be quiet and she would be able to go back to her book.

Outside the windows farmland passed by. Trees and fields. Glinda had lost count of how many cows she had seen. "What would you name a baby?"

"What?!" Elphaba dropped the book, loosing her page. Please say she didn't just say that.

"Oh!" The blonde one yelped, and she giggled. "Don't worry." Now she was offended."I'm too much of a lady to do that before I get married. Did you really think...?" She trailed off, ready to pitch a fit that her best friend had accused her of having premarital sex.

Elphaba gave her a look. She mimicked her roommate's voice, perfectly. "Fiyero and I are going to be married!" Then, in her own voice, she added, "Really, Glinda, if you're so sure you'll marry him after knowing him for one day, I can't see children being too far out of your pretty little head after a few weeks. Why did you ask me that, anyway?"

"Well, my brother's wife is having a baby, and they haven't picked a name yet. I was just wondering what you would name a baby."

The food cart rolled past but the girls paid it no mind. Elphaba smirked. "Glinda." She laughed then. "How did your parents name you?"

"After my Great-Aunt. And you?"

Elphaba frowned. "I was 'Dragon-Girl' for about a week. They were hoping I'd die, I think. Then my mother decided I was too healthy for my own good and my father flipped to a random page in the Oziad. It was the story about some Saint who, among other saintly things, hid behind a waterfall and prayed. I think grapes were involved, somewhere."

Glinda grimaced at Elphaba's matter-of-fact declaration that her parents had wished she had died at birth. "Well, Elphaba is a pretty name." She brightened. "Maybe I should tell my brother to name his daughter after you!"

"You wouldn't. No one wants to be named after me."

---

Not quite ten years later, after Oz had settled down after the events of the Witch Hunt, Glinda the Good had her first child, a little girl who rarely fussed and was fascinated with life itself. She named her Elphaba, knowing no one would accuse her of naming the child after the Witch of the West. To most of Oz, the Witch had had no name herself.