1. Any of several prickly pears; especially, a treelike pear of tropical America with an edible fruit or the fruit itself: When Mary was in her biology class the other day, the class read about tuna, which is also a kind of cactus, not only a fish!

Mary also found out that the fruit of this cactus, especially that of the Opuntia tuna of Jamaica, had spiny flat connections between the flat leaves, had fruit that was oval and red, and was used primarily as food for livestock.

2. Etymology: from American Spanish and previously from Taino.