The word "fit" has been around since Old English (and probably before then, too, but this is an English language class). To the right, I've listed a sampling of the OED definitions for "fit" in various parts of speech.
Since there are so many different uses of the word and my time, unfortunately, is limited, I decided to focus on a few fun phrases involving "fit" as well as a few other samplings of corpus data related to my searches.
In a fit of .
This use of "fit" probably comes from a now-obsolete usage that referred to "fits" as insanity. A fit would 'seize' someone, and they'd lose control, convulse, etc. Here are some of the results of corpus searches with this phrase.
In a fit of . Simply a list of all the things you can have a fit of. Some of my favorites are pique, jealousy, delirium, and frustration.
1950s-2000 compared to 1800s Here I looked at "in a fit of " in two time periods to compare what people used to fill in the blank. I personally really liked the older words (on the right of the search results). You never seem to hear about a "fit of desperation" or a "fit of hysterics" or a fit of musing" anymore, and what a shame that is!
Similar and related phrases:
By fits and starts - to use the OED's definition, this means to do something "spasmodically" (which is really a great word, don't you think?).
Temper tantrums: All the ways to say someone threw a fit. (Also in there are things like "to be a fit," as in a match to something, or the fitting of clothes.)
Fit to be tied, seen, and all such phrases. This one reminds me of Foghorn Leghorn, but maybe that's just because I listened to too much of the Looney Tunes Christmas CD when I was a kid. He makes a joke about "Well, you'll be fit to be tied... Get it? You'll... Tied... .Yule Tide?" Lame jokes aside, I thought this was a dying phrase, but the corpus proved me wrong. Go figure.
fit.[j*] and . There are many phrases to say someone's healthy. But when was the last time some answered, "I'm healthy, thanks" when you asked how they're doing? You're more likely to hear fit and well, fit as a fiddle (which, by the way, led me to the fun expression of "fiddling while Rome burns"), fit and trim, and so forth. Here are some other things you can be "fit as."
"All the news that's fit to print." Coined in 1897, this phrase has been the New York Times' motto for many, many years, and is a great example of a particular adjectival use of "fit." It's not "athletic" news, it's not "form-hugging clothing" news, it's not "puzzle piece" news; it's "proper, respectable, and agreeable to decorum" news. Here are some other "fit to [v*]" expressions.
Things and ways you can "fit in" (not into). I thought it was interesting to see how you can "fit someone in" for your schedule, a phrase that seemed to spike in the 1960s and then die off. I thought it would have been a more recent usage, but once again I was proven wrong.