Tiny chest? Bust is false (9)
I believe the answer is:
synthetic
'is false' is the definition.
(thesaurus)
'tiny chest? bust' is the wordplay.
'bust' is an anagram indicator.
'tiny'+'chest'='tinychest'
'tinychest' with letters rearranged gives 'SYNTHETIC'.
(Other definitions for synthetic that I've seen before include "Not genuine, unnatural" , "Manufactured, not produced naturally - say material" , "Man-made (fibre)" , "Man-made, not natural" , "Artificially-made compound" .)