Family

A family of languages (or language family) is a group of languages that have developed from a common ancestor.

Comments
Some linguists have tried to establish separate terms for larger and smaller groups of languages, or for groups with greater and shallower time-depth. None of these are as universally accepted and used as family. Here are some of them:
 * stock, super-stock
 * phylum
 * genus

Origin
This term was apparently adopted by linguists from biology, where a group of similar plants had been called family since the mid-18th century, if not earlier. The term is deeply entrenched in linguistics since at least the mid-19th century.

Other languages
German Sprachfamilie