Dictionary.net

• A proteid decomposition product.

1920 - A dictionary of scientific terms.
By Henderson, I. F.; Henderson, W. D.

• An amino acid derived from cystin. It is alpha-amino-beta-thiolactic acid, CH2 (SH)CH (NH2 )COOH. [Fr.]

1916 - Appleton's medical dictionary
By Smith Ely Jelliffe