These key political and financial terms are sometimes confused. 'Deficit' is when spending exceeds income; 'debt' is the accumulated 'deficits' to date. Both words are Latin in origin, though 'debt' has been with us longer. It derives from debitum, which itself comes from the verb debere, to owe: in other words, it means 'the thing owed'. 'Deficit', on the other hand, comes from deficere, to fail, lack or undo, and means 'it is wanting'. Figurative uses are allowed: explain the difference and you can remedy a 'deficit' in someone's understanding and leave him in your 'debt'.