Usury is derived from the Latin word usura, defined as "a sum paid for the use of money."
The early Christians were unanimous in regarding all interest as usury, and, therefore, as a species of robbery.
Whatever exceeds the amount owed is usury. Usury occurs when more is demanded back than what is given.
Tertullian considers the subject of interest in his treatise on the theology of the New Testament, Adversus Marcionem, where he teaches that the Gospel does not abolish the law of the Old Testament, it exceeds it. Tertullian writes of the just man, "He hath not...put out his money at interest, and will not accept any increase - meaning the excess amount due to interest, which is usury."