A Few Words I Don't Think We Use Enough
Since English is such a flexible language, it grows by leaps and bounds with every passing day - Oxford thinks there may be as many as three quarters of a million different words (including inflections) that could be considered English. (here).

So, of course, there are a few words we're likely to stop using. The average English speaker (who's likely not to have learned English as a first language, since 52% of English speakers didn't) recognize 10,000 words or so; the average native recognizes about 20,000.

So here are a few words I think we should use a bit more often:
1) Brobdignagian - Big. Really, really big.
2) Tomfoolery - Unadvisable behavior.
3) Unadvisable - Uhm....yeah.
4) Philistine - Smug, ignorant person. Best used by Daffy Duck.
5) Offal - Cast-off innards, or undesirable byproducts.
6) Jezebel - Scheming, greedy woman.
7) Apoptotic - Of or relating to programmed cell death. There has GOT to be a way to work this into everyday conversation.
8) Drudgery - Menial labor. Unexciting activities.
9) Hoar - Frost that forms sharp white crystals out of doors. See also: Canada. Can also be used as a color.
10) Defunct - Kaput.

So there's 10 words for you that you should try to use more often. It makes other people feel stupid, which is a nice feeling.