Act weakly to have debts seized by creditor (5)
I believe the answer is:
cower
'act weakly' is the definition.
'to have debts seized by creditor' is the wordplay.
'to have debts' becomes 'owe'.
'seized by' means one lot of letters goes inside another.
'creditor' becomes 'cr'.
'owe' placed into 'cr' is 'COWER'.
(Other definitions for cower that I've seen before include "intimidating person?" , "Cringe, grovel" , "Show abject fear" , "to emulate Burns's wee beastie" , "Cringe in fear" .)