Nuts are able to expand (9)
I believe the answer is:
elaborate
'expand' is the definition.
(I know that expand can be written as elaborate)
'nuts are able to' is the wordplay.
'nuts' is an anagram indicator (nuts can mean crazy).
'are'+'able'+'to'='areableto'
'areableto' is an anagram of 'ELABORATE'.
(Other definitions for elaborate that I've seen before include "Add details to clarify meaning" , "Present in further detail" , "Ostentatious, possibly" , "Complicate" , "Fussy" .)