Worried by debts one's taken on in advance (7)
I believe the answer is:
anxious
'worried' is the definition.
(I've seen this before)
'debts one's taken on in advance' is the wordplay.
'debts' becomes 'IOUs' (promises to pay debts).
'one' becomes 'an' (an apple is one apple).
'taken on' becomes 'x' (I am not sure about this - if you are sure you should believe this answer much more).
'in advance' says to put letters next to each other.
'an'+'x'='anx'
'ious' put after 'anx' is 'ANXIOUS'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for anxious that I've seen before include "Jittery" , "Restless" , "Fretful, worried" , "On edge" , "Nervy" .)