The answer, you can depend, is soft-hearted (5)
I believe the answer is:
reply
'the answer' is the definition.
(synonyms)
'you can depend is soft-hearted' is the wordplay.
I cannot really see how this works, but
'soft' could be 'p' (musical abbreviation for 'piano') and 'p' is present in the answer.
'depend' could be 'rely' (to depend on someone is to rely on them) and 'rely' is present in the remaining letters.
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 reply that I've seen before include "Returned statement" , "Reciprocate" , "Retort" , "response is demanded" , "Comeback" .)