(1) Sympathy; attraction. (2) Relationship.
Example:
He knew of Carl's affinity to both wine and violence, and intended to take advantage of them.
Affinity gives a sense of things touching along their boundaries and therefore being of interest to each other. Felix Mendelssohn showed an affinity for music at a very early age and composed several fully developed symphonies while still in his teens; Stevie Wonder revealed his own musical affinity long before he made his debut at the age of 10. A strong affinity for another person may deepen into love. A critic may notice affinities between the works of two writers. A naturalist may speak of the affinity between two bird species -- that is, their close physical relation to each other.