Noah Webster
Set-off
SET'-OFF, noun [set and off.] The act of admitting one claim to counterbalance another. In a set-off the defendant acknowledges the justice of the plantif's demand, but sets up a demand of his own to counter balance it in whole or in part.
The right of pleading a set-off depends on statute. Blackstone.
NOTE.- In new England, offset is sometimes used for set-off. But offset has a different sense, and it is desirable that the practice should be uniform, Wherever the English is spoken.