Animal, vegetable, plant (11)
I believe the answer is:
horseradish
'plant' is the definition.
(horseradish is a kind of plant)
'animal vegetable' is the wordplay.
'animal' becomes 'horse' (type of animal).
'vegetable' becomes 'radish' (radish is a type of vegetable).
'horse'+'radish'='HORSERADISH'
(Other definitions for horseradish that I've seen before include "that's hot" , "type of sauce" , "Source of sauce to go with beef" , "Saucy root vegetable?" , "Root used in sauce" .)