Promise.

"It's just a ring," she said flatly. "A band of silver with a few embellishments. Size six. Scratches have undoubtedly been polished out of it." She considered it for a moment, twisting it around the finger it sat humbly upon. "Cool to the touch. Smooth. Circular."
"You look at things so strangely sometimes," I told her. She gave me a furtive frown.
"Oh? How so?"
Gently, I reached over and laid my hand over hers. "It's not just a piece of metal. It's a promise."