To tithe is to make a contribution equal to one-tenth of your income, usually to a church or religious institution. You probably always tithe, even in years when your 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.