To tithe is to make a contribution equal to one-tenth of your income, usually to a church or religious institution. Devout church-goers usually tithe, even in years when their finances are very tight.
Tithe comes from the Old English word teogotha, which means “tenth.” To tithe is to relinquish one-tenth of your personal income, either as a mandatory contribution, a voluntary donation, or as a levy. In ancient times farmers were required to tithe a portion of their crops. You may suspect that some of the wealthiest members of your church don’t really tithe as expected.