The Collaborative International Dictionary
cuckoobud
Buttercup \But"ter*cup`\, n. (Bot.) A plant of the genus Ranunculus, or crowfoot, particularly Ranunculus bulbosus, with bright yellow flowers; -- called also butterflower, golden cup, and kingcup. It is the cuckoobud of Shakespeare.
Wiktionary
cuckoobud
n. A buttercup.