Nut Newton going nuts (6)
I believe the answer is:
noggin
'nut' is the definition.
(thesaurus)
'newton going nuts' is the wordplay.
'newton' becomes 'n' ('N' can be a synonym of 'newton').
'nuts' indicates an anagram (nuts can mean crazy).
'going' anagrammed gives 'oggin'.
'n'+'oggin'='NOGGIN'
(Other definitions for noggin that I've seen before include "alcoholic drink?" , "Small measure of spirits or mug" , "Small mug - wooden cup" , "Peg" , "spirited measure" .)