Definitions of affinity:

• noun:   a natural attraction or feeling of kinship

  Example: "An affinity for politics"

• noun:   inherent resemblance between persons or things
• noun:   the force attracting atoms to each other and binding them together in a molecule

  Example: "Basic dyes have an affinity for wool and silk"

• noun:   (immunology) the attraction between an antigen and an antibody
• noun:   a close connection marked by community of interests or similarity in nature or character

  Example: "Found a natural affinity with the immigrants"

• noun:   (biology) state of relationship between organisms or groups of organisms resulting in resemblance in structure or structural parts

  Example: "In anatomical structure prehistoric man shows close affinity with modern humans"

• noun:   kinship by marriage or adoption; not a blood relationship