Owing to strain, cashier Sibyl (7-6)
I believe the answer is:
fortune-teller
'sibyl' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'owing to strain cashier' is the wordplay.
I cannot quite see how this works, but
'to' could be 'for' and 'for' is found within the answer.
'strain' could be 'tune' (synonyms) and 'tune' is present in the answer.
'cashier' could be 'teller' (synonyms) and 'teller' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for fortune-teller that I've seen before include "Palm reader" , "Clairvoyant, future diviner" , "Soothsayer" , "User of crystal ball" , "Predictor of one's future" .)