link "Noun: A logical or natural association between two or more things.
relation,
relationship,
connection,
correlation,
interrelation,
interdependence,
interrelationship,
tie-in,
interconnection.Verb: To unite or be united in a relationship.
(from Roget's II Thesaurus)
join,
relate,
associate,
combine,
bind,
connect,
ally,
affiliate,
conjoin."