Noun
1. The study of cells and tissue on the microscopic level. (biology-online.org)
2. The study of the microscopic anatomy of cells and tissues of plants and animals. It is commonly performed by examining cells and tissues by sectioning and staining, followed by examination under a light microscope or electron microscope. (wikipedia.com)
Word origin: Compound of the Greek words: ἱστός “tissue”, and -λογία -logia