1. Mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones. (wikipedia.org)
2. A person’s capacity to break down food in such a way. (Google Dictionary)
3. The process of treating a substance by means of heat, enzymes, or a solvent to promote decomposition or extract essential components. (Google Dictionary)
Word origin: Borrowed from Latin digestio, digestionem.