From Borstal, a ghastly prison (6)
I believe the answer is:
stalag
'prison' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I don't see?
'from borstal a ghastly' is the wordplay.
'from' says the answer is hidden in the clue.
'STALAG' is hidden in the letters of 'borstal a ghastly'.
Can you help me to learn more?
(Other definitions for stalag that I've seen before include "German POW camp in WWII" , "German prison_camp" , "WWII German prisoner of war camp" , "German prisoner-of-war camp of WW2" , "German concentration camp" .)