Unpalatable cases initially cause revulsion beyond belief (10)
I believe the answer is:
incredible
'beyond belief' is the definition.
(incredible literally means impossible to believe)
'unpalatable cases initially cause revulsion' is the wordplay.
'unpalatable' becomes 'inedible' (unpalatable can mean not very nice to eat).
'cases' indicates putting letters inside (forms a case around).
'initially' indicates taking the first letters.
The first letters of 'cause revulsion' is 'cr'.
'inedible' going around 'cr' is 'INCREDIBLE'.
(Other definitions for incredible that I've seen before include "Beyond belief" , "Fantastic" , "Impossible to believe" , "Unbelievable" .)