in Botany, thorns, rigid prickles: a species of arna, growing on various parts of certain plants for their defence; spinæ ramorum arcent pecora. On the branches we find examples in the pyrus, prunus, citrus, hippophaes, gmelina, rhamnus, lycium, &c.; on the leaves, in the aloe, agave, yucca, ilex, hippomane, theophrasta, carlina, &c.; on the calyx, in the carduus cynicus, centaurea, moluccella, galeopsis, &c.; on the fruit, in the trapa, tribulus, murex, spinacia, agrimonia, datura, &c.