What is a crown of thorns? Here are some definitions.
Noun
(Christianity) The crown made of a thorny plant that Christ was forced to wear before his Crucifixion, in mocking reference to his alleged status as ‘king of the Jews’, or a representation of this. [from 10th c.]
A spiny Mediterranean tree, Ziziphus spina-christi. [from 19th c.]
A spiny spurge, Euphorbia milii, native to Madagascar. [from 19th c.]
A large starfish with venemous spines, Acanthaster planci. [from 20th c.]