association

Concise Oxford English Dictionary © 2008 Oxford University Press:
association/əsəʊʃiˈeɪʃn/

▶noun

• 1 a group of people organized for a joint purpose.

• 2 a connection or cooperative link between people or organizations.

  ■ Chemistry a weak interaction between molecules, such as hydrogen bonding.

• 3 a conceptual connection.

• 4 Ecology a stable plant community including a characteristic group of dominant plant species.

– derivatives
associational adjective.