Business undertaking to cause anxiety (7)
I believe the answer is:
concern
I believe this clue is a triple definition!
'business' is the first definition.
(eg 'none of your concern', 'none of your business')
'undertaking' is the second definition.
(thesaurus)
'to cause' is a link.
'anxiety' is the third definition.
(I know that concern is a type of anxiety)
(Other definitions for concern that I've seen before include "Disquiet" , "Have something to do with" , "Cause of anxiety" , "Relate to; anxiety" , "Feeling of anxiety or sympathy" .)