It's shrewd to stifle a triumphant cry on one's own (6)
I believe the answer is:
solely
'on one's own' is the definition.
Both the answer and definition are adverbs. Perhaps you can see a link between them that I can't see?
'it's shrewd to stifle a triumphant cry' is the wordplay.
'it's shrewd' becomes 'sly' (I've seen this in another clue).
'to stifle' means one lot of letters goes inside another.
'a triumphant cry' becomes 'ole' (I've seen this in another clue).
'sly' placed around 'ole' is 'SOLELY'.
Can you help me to learn more?
(Other definitions for solely that I've seen before include "Singly" , "nowhere else?" , "Exclusively, only" , "Singularly" , "alone" .)