Ascetic scoffed about American soldiers (7)
I believe the answer is:
austere
'ascetic' is the definition.
('austere' can be a synonym of 'ascetic')
'scoffed about american soldiers' is the wordplay.
'scoffed' becomes 'ate' ('to scoff' is to eat).
'about' indicates putting letters inside.
'american' becomes 'us'.
'soldiers' becomes 're' (Royal Engineers).
'ate' going around 'us' is 'auste'.
'auste'+'re'='AUSTERE'
(Other definitions for austere that I've seen before include "Grim - USA tree (anag)" , "Severely simple and plain in appearance" , "Severe, ascetic" , "Severe or strict in attitude" , "Severe in manner" .)