1 : (chemistry) two or more atoms bound together as a single unit and forming part of a molecule
2 : an unofficial association of people or groups
3 : a smallest army unit
4 : (biology) taxonomic group containing one or more species
5 : an association of companies for some definite purpose
6 : an informal body of friends
7 : a collection of things sharing a common attribute
8 : a grouping of a number of similar things