As an English major, Linguistics 101 was a required course. Surprisingly, I actually loved the class . . . though that might have been because the teacher was a stand-up comedian on the side.
So of all the things I'm sure I should have learned from that class, what I best remember are Lexical Gaps.
Lexical Gaps, in the linguistic sense, are possible word forms which aren't really words. Sometimes it's because another word already exists to express the same meaning, sometimes there's no real reason. It just isn't.
Examples would be funner, badder, goodest, extinctified, unreplaceable, fantabulous.
Granted, some lexical gaps are a bit grating (i.e. goodest, badder, funner), but used right, they can liven things up and give a sense of personality. I've seen a couple on blogs that are fun: besties, awesomesauce.
So the question is, do you have a favorite lexical gap? And would you ever use it in your book?
P.S. Now when someone tells you "That's not a word," you can tell them, "Yes, but it's a lexical gap, so I can use it." :D