Disgust American by rolling tongue (5)
I believe the answer is:
appal
'disgust' is the definition.
(appalling is a kind of disgusting)
'american by rolling tongue' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'by' is a charade indicator (letters next to each other).
'rolling' is a reversal indicator.
'tongue' becomes 'lapp' (Lapp is an example).
'lapp' back-to-front is 'ppal'.
'a'+'ppal'='APPAL'
(Other definitions for appal that I've seen before include "To shock, dismay" , "Greatly dismay" , "Scandalise" , "Petrify" , "Greatly horrify" .)