What science word means "to group"?

The science word that means “to group” is classify.

To classify means to arrange people, objects, organisms, or ideas into groups according to shared features. Scientists classify things so that complex information becomes easier to identify, compare, study, and communicate. A biologist might classify an organism by its cell structure, genetics, anatomy, or evolutionary relationships.

Classification is closely related to taxonomy, the scientific discipline concerned with naming and organizing living things. In the familiar Linnaean hierarchy, organisms are placed into ranks such as domain, kingdom, phylum, class, order, family, genus, and species. The verb classify describes the action; classification describes the process or its result; and a class is one of the groups created.

A common mix-up is treating classify and identify as synonyms. Identification determines what something is, while classification places it into a relevant group. For example, recognizing an animal as a gray wolf is identification; placing it in the mammal, carnivore, and Canidae groups is classification. Modern biology increasingly uses DNA and evolutionary history when making those groupings.