Uncle's cut off a cactus? (9)
I believe the answer is:
succulent
'a cactus?' is the definition.
(cactus is a kind of succulent)
'uncle's cut off' is the wordplay.
'off' indicates an anagram.
'uncles'+'cut'='unclescut'
'unclescut' anagrammed gives 'SUCCULENT'.
(Other definitions for succulent that I've seen before include "Full of juice" , "Juicy" , "Luscious" , "Eg, a cactus" , "One may be potted!" .)