Definition from Wiktionary, the free dictionary
buttercup (plural buttercups)
- Any of many herbs, of the genus Ranunculus, having yellow flowers; the crowfoot.
- Any flower of the genus Narcissus; a daffodil
- Affectionate or ironic term of address.
1987, Joyce Brandon, Lady and the Lawman, page 346:
- Listen, buttercup, you're damned good in bed. They don't come any better, but I'm really not interested in playing second fiddle to your camera or your young lovers.
herb of the genus Ranunculus
flower of the genus Narcissus — see daffodil