affinity

Where it comes from

Affinity ordinarily means a natural liking, connection, or similarity between people or things. Affinity came through Anglo-French from Latin affinitas. Its adjective affinis combined ad-, toward or adjoining, with finis, boundary: it meant bordering on and, by extension, related through marriage. Marriage brought two families into contact without making them blood relatives, so legal affinity contrasted with consanguinity.

How the meaning developed

The idea of connection then widened to resemblance, sympathy, attraction, and finally the tendency of chemical substances to combine.

In use

One is a close connection. The other has no end.
Which fits: She felt an immediate ______ with the city?

“Affinity” means a natural connection or similarity. “Infinity” means endlessness or something without limit.
You can have an affinity for mathematics without understanding infinity.