Discourage current measure supporting source of debt (4)
I believe the answer is:
damp
'discourage' is the definition.
(thesaurus)
'current measure supporting source of debt' is the wordplay.
'current measure' becomes 'amp' (I've seen this before).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'source of' indicates taking the first letters.
The initial letter of 'debt' is 'd'.
'amp' after 'd' is 'DAMP'.
(Other definitions for damp that I've seen before include "Clammy" , "Rising -, TV sitcom" , "Moisture" , "Humid" , "Moist air" .)