Definition of Christmas cactus in English:

Christmas cactus

noun

  • A South American cactus with flattened segmented stems and red, pink, or white flowers, grown as a houseplant.

    • ‘Every fall, my Christmas cactus displays a spectacular profusion of blooms on a covered patio in San Mateo, California.’
    • ‘While poinsettia is the most popular, a Christmas cactus in full bloom is a great gift and easy to care for once the flowers have faded.’
    • ‘You'll be glad to hear that my Christmas cacti are now dripping with pink buds and the geraniums on my frost-free balcony continue to bloom spectacularly.’
    • ‘The best flowers to give at Christmas time are orchids, holly, poinsettias, and the Christmas cactus as well as any red flower.’
    • ‘And remember to get your poinsettias and your Thanksgiving and Christmas cacti ready for well-timed holiday color.’

Origin

So named because it flowers at about the northern midwinter.