Other forms: cacti, cactuses
A cactus is the desert plant covered in spines that survives on almost no water. A potted cactus, a cactus in flower, prickly as a cactus.
The plural is cacti or cactuses, both correct. What makes a plant a cactus is a structure called an areole, the small cushion the spines grow from — which is why not every spiny succulent is one. The spines are modified leaves; the stem does the photosynthesis and stores the water. Cacti are native to the Americas only, apart from one species, so any cactus in an African desert scene is a mistake.
1nouncactusA desert plant covered in spines that needs almost no water.
“The cactus on the windowsill has survived four house moves.”
cactus is a plant.
Greek kaktos was the name of a spiny plant of Sicily, probably the cardoon — nothing to do with the American plants at all. Linnaeus applied the old name to the new family, which is why the word is Greek for something the Greeks never saw.
Ancient Greek
κάκτος — cardoon
Latin
cactus
mul-tax
Cactus
Translingual
Cactus
English, today
cactus
Borrowed from Translingual Cactus. From mul-tax Cactus, a name given in 1752 by Linnaeus for a genus of cacti (now superseded by the genus name Mammillaria), from Latin cactus, from Ancient Greek κάκτος (“cardoon”), possibly of qsb-grc origin.
Etymology from Wiktionary, CC BY-SA