Whole nuts in tree (6)
I believe the answer is:
entire
'whole' is the definition.
(similar in meaning)
'nuts in tree' is the wordplay.
'nuts' indicates anagramming the letters (nuts can mean crazy).
'in'+'tree'='intree'
'intree' anagrammed gives 'ENTIRE'.
(Other definitions for entire that I've seen before include "Unmitigated" , "Whole and complete" , "Whole; absolute" , "Unharmed - total" , "porter" .)