From opheilo; an ower, i.e. Person indebted; figuratively, a delinquent; morally, a transgressor (against God) -- debtor, which owed, sinner.
see GREEK opheilo
a. one held by some obligation, bound to some duty: ὀφειλέτης εἰμί, equivalent to ὀφείλω, followed by an infinitive, Galatians 5:3 (Sophocles Aj. 590); ὀφειλέτης εἰμί τίνος, to be one's debtor i. e. under obligations of gratitude to him for favors received, Romans 15:27; τίνι (dative commodi), to be under obligation to do something for someone, Romans 1:14; Romans 8:12.
b. one who has not yet made amends to one whom he has injured: Matthew 6:12; in imitation of the Chaldean חַיָב, one who owes God penalty or of whom God can demand punishment as something due, i. e. a sinner, Luke 13:4.