[1] : The Collaborative International Dictionary of English v.0.48

cactus \cac"tus\, n.; pl. e. cactuses, cacti -timac.
   l., a kind of cactus, gr. ??????. bot.
   any plant of the order cactacae, as the prickly pear and
   the night-blooming cereus. see cereus. they usually have
   leafless stems and branches, often beset with clustered
   thorns, and are mostly natives of the warmer parts of
   america.
   1913 webster

   cactus wren zool., an american wren of the genus
      campylorhynchus, of several species.
      1913 webster
see also:
cactuses cacti cactacae cereus cactus wren campylorhynchus 

[2] : WordNet (r) 2.0

cacti
     see cactus
see also:
cactus 

[3] : WordNet (r) 2.0

cactus
     n : any spiny succulent plant of the family cactaceae native
         chiefly to arid regions of the new world
     also: cacti pl
see also:
cacti 

Cacti >> C Words
Cacti, definition of term: Cacti
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