Definitions for joshua tree
Random House Webster's College Dictionary
an evergreen tree, Yucca brevifolia, with long, twisted branches, growing in arid regions of the southwestern U.S.
Joshua tree, Yucca brevifolia(noun)
a large branched arborescent yucca of southwestern United States having short leaves and clustered greenish white flowers
A yucca, Yucca brevifolia, of the southwestern U.S. with spiky leaves.
Origin: Apparently from the resemblance of the tree to Joshua holding out his spear (Joshua 8:18: ‘And the LORD said unto Joshua, stretch out the spear that is in thy hand toward Ai; for I will give it into thine hand. And Joshua stretched out the spear that he had in his hand toward the city.’ KJV).