Not only is this a useful word, it’s fun to say. Try it aloud: propinquity. There’s something light and leaping about the experience, like a chickadee hopping from branch to branch. (Ok, so I may be in this mood because I just replenished the seed in the bird feeder.)
It comes from the Latin propinquus, near or neighboring, and it means a closeness or proximity. It has also been used to signify a nearness in time, not just distance. In addition, it can refer to kinship or to similar dispositions or belief.
Variations include propinquant (adjacent), propinquate (proximate), propinquous (close at hand), and the obsolete propinque (immediate, proximate). In sociology, researchers study the Propinquity Effect.
I was surprised and delighted to discover a rare antonym: longinquity, remoteness in space or in time. I think that’s a word that deserves to be revived. It is related to the also rare longinque (distant).
SIDEBAR: The Edge of Propinquity
(substitute @ for AT above)