Sanity of Chisholm in doubt (4)
I believe the answer is:
mind
'sanity' is the definition.
(thesaurus)
'of chisholm in doubt' is the wordplay.
'of' indicates a hidden word.
'MIND' is hidden within 'chisholm in doubt'.
(Other definitions for mind that I've seen before include "Intelligence" , "Inclination" , "Watch - intellect" , "Object to; take care of" , "Intellect; object to" .)