Here are two sentences I have extracted from Google dictionary, both containing the word against, under the meaning of offset.
First usage sentence is under noun offset, sense 1:
"widow's bereavement allowance is an offset against income"
What does offset against income mean?
- Widow's bereavement allowance is given because they don't get income.
- Widow's bereavement allowance is given in addition to income because of their deprived situation.
Second sentence is given under verb offset, sense 1:
"donations to charities can be offset against tax"
What does offset against tax mean?
I don't get any interpretation at all.