It's poor relief; be cautious about it (7)
I believe the answer is:
charity
'it's poor relief' is the definition.
I can't tell whether this defines the answer.
'cautious about it' is the wordplay.
'cautious' becomes 'chary' (similar in meaning).
'about' means one lot of letters goes inside another.
'chary' placed around 'it' is 'CHARITY'.
'be' is the link.
Can you help me to learn more?
(Other definitions for charity that I've seen before include "Help for needy" , "Benevolence" , "Pecksniff girl" , "Gifts to the needy" , "Giving to the needy" .)