Noun
1. The branch of biology that deals with the formation, structure, and function of cells. (The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company.)
2. The study of cells, their origin, structure, function and pathology; it implies the use of light or electron microscopic methods for the study of morphology, and as a means to diagnose or test for cancer and other diseases. (Biology-online.org)
Word origin: from Greek κύτος, kytos, a hollow + -λογία, -logia