off·set 1 /'ȯf-ˌset/ n: a claim or amount that reduces or balances another claim or amount: set-off
the creditor's own debt was an offset; also: the reduction or balance achieved by such a claim
off·set 2 /ˌȯf-'set/ vt: to balance, reduce, or calculate by reference to another amount
offset the debt against a credit
Merriam-Webster’s Dictionary of Law. Merriam-Webster. 1996.