Noun, pl. cells
1. The functional basic unit of life (Wikipedia.com)
2. The smallest structural and functional unit of an organism, typically microscopic and consisting of cytoplasm and a nucleus enclosed in a membrane. Microscopic organisms typically consist of a single cell, which is either eukaryotic or prokaryotic. (dictionary.com)
3. The fundamental unit of all living tissue. Eukaryotic cells consist of a nucleus, cytoplasm, and organelles surrounded by a plasma membrane. Within the nucleus are the nucleolus (containing ribonucleic acid) and the chromatin (containing protein and deoxyribonucleic acid), which form chromosomes, wherein are located the determinants of inherited characteristics.
Organelles within the cytoplasm include the endoplasmic reticulum, ribosomes, Golgi apparatus, mitochondria, lysosomes, and centrosome. Prokaryotic cells are much smaller and simpler than eukaryocytic cells, even lacking a nucleus. The specialized nature of body tissue reflects the specialized structure and function of its constituent cells. (Mosby’s Medical Dictionary, 8th edition. © 2009, Elsevier.)
Word origin: From Old English *cella (attested in inflected forms), from Latin cella (“chamber, small room, compartment”), later reinforced by Anglo-Norman cel, sele, Old French cele.