Chemistry A group of elements with similar chemical properties. A fundamental social group in society typically consisting of one or two parents and their children. Two or more people who share goals and values, have long-term commitments to one another, and reside usually in the same dwelling place. All the members of a household under one roof. A group of persons sharing common ancestry. See Usage Note at collective noun. Lineage, especially distinguished lineage. A locally independent organized crime unit, as of the Cosa Nostra. A group of like things; a class. A group of individuals derived from a common stock: the family of human beings. Biology A taxonomic category of related organisms ranking below an order and above a genus. A family usually consists of several genera. See Table at taxonomy. Linguistics A group of languages descended from the same parent language, such as the Indo-European language family. Mathematics A set of functions or surfaces that can be generated by varying the parameters of a general equation. Chemistry A vertical column in the periodic table of elements. Of or having to do with a family: family problems. Being suitable for a family: family movies.