Vile soldiers dog grandmother without end (9)
I believe the answer is:
repugnant
'vile' is the definition.
(I've seen this before)
'soldiers dog grandmother without end' is the wordplay.
'soldiers' becomes 'RE' (Royal Engineers).
'dog' becomes 'pug' (pug is a kind of dog).
'grandmother' becomes 'nan' (nan can informally mean a grandmother).
'end' says to take the final letters.
The final letter of 'without' is 't'.
're'+'pug'+'nan'+'t'='REPUGNANT'
(Other definitions for repugnant that I've seen before include "Extremely distasteful" , "Loathsome" , "Abhorrent" , "Nasty" , "Disgusting" .)