The world of plants and animals (6)
I believe the answer is:
nature
'the world of plants and animals' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nature that I've seen before include "Essential character" , "The external, untouched world" , "Character, make-up" , "mother, so-called" , "All non-artificial phenomena" .)