propinquity
Use this word when you want to seem smart – or stupid. It's your choice, really. (It's all just a big game of fortuna, as it's the other people that form their opinion on you and you cannot really affect that process.) It's the type of word you only see on the "most searched" list of dictionary.com and on Yahoo!'s headlines (the latter-mentioned explains the first-mentioned).

People who have to look up this word are either too smart or "too dumb" and if this being the case, they are also very likely to read Yahoo! News. Why Yahoo! in the first place uses words that are understood only by 0.01‰ (1 out of 100 000) of the population, remains yet unclear. But when you are seen to use this word, people will know (if they're intelligent enough) that you got it from nowhere else than Yahoo! News...
Woody: "The propinquity of these – pardon my sterile approach on the topic – two given objects is inversely proportional to..
Bob: "Why don't you just say "approximity" or "distance" or something?"
Woody: "W-what? I don't.."
Bob: "Yes, you do. Don't play stupid."
Gary: "Yeah, man. Don't use words that are understood only by 3500 Americans – that's what Yahoo! News does."