Heroin American beat combo use thriftily (7)
I believe the answer is:
husband
'use thriftily' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'heroin american beat combo' is the wordplay.
'heroin' becomes 'H' (H is a slang term for heroin).
'american' becomes 'US' (abbreviation for United States).
'beat combo' becomes 'band' (I've seen this in another clue. I am not sure about the 'beat' bit.).
'h'+'us'+'band'='HUSBAND'
Can you help me to learn more?
(Other definitions for husband that I've seen before include "Spouse - save" , "Male relative" , "Consort" , "Be thrifty with" , "Economically manage" .)