The little word fit has multiple functions and occurs in numerous expressions.
In Middle English, the noun fit denoted an intense experience that could be painful, dangerous, or exciting.
By the 16th century, a fit could denote a paroxysm, or the recurrent attack of an ailment.
In the 17th century fit took on the meaning of a sudden seizure with loss of consciousness, or accompanied with convulsions.
By the 19th century, fit was used in expressions of exaggeration such as “to throw a fit” in the sense of “to fly into a rage.”
Because fits are of limited duration, the noun fit also took on the sense of a limited, usually brief, period of time: “We’ve had a fit of wet weather.”
Fit also functions as an adjective: a synonym for appropriate or well-suited. For example, a man might be “fit for a certain job,” or a certain type of food might be “fit for an invalid.” Fit can also mean inclined or disposed. A tired person might be “fit to collapse.” An angry person might be “fit to be tied.” A child trying to keep a secret might be “fit to burst.”
Fit (and fitting) also applies to social behavior. In Gone With the Wind, the character Mammy uses the word in this sense when she reprimands Scarlett for unladylike behavior: “It ain’t fittin; it just ain’t fittin’.”
In the 19th century, fit took on the meaning “in good health” or “in good physical condition.” People go to the gym “to get fit.”
As a verb, in addition to meanings related to those mentioned, fit can mean “to be of the right shape and size.”
Here are some common expressions that use the word fit:
to have a fit
to become upset about something
Ex. Don’t have a fit; I’ll make your sandwich in a minute.
an outburst of temper, a tantrum. Hissy may be a shortening of hysterical.
Ex. Aunt Ida is having a hissy fit; somebody broke her garden gnome.
survival of the fittest
The expression was coined by Herbert Spencer in reference to the Darwinian theory that animals best-adapted to an environment continue to reproduce and evolve. In this context, “the fit” are those animals suited to succeed. It is frequently used figuratively.
Ex. In cable, it’s survival of the fittest as channels drop from the bundle.
in fits and starts
spasmodically; at irregular intervals.
Ex. He’s been cleaning the garage in fits and starts.
fit to be tied
Ex. When Father saw someone had left the gate open, he was fit to be tied.
at the peak of one’s physical form
Ex. Papiss Cisse says he’s fighting fit to help lead the charge against Queens Park Rangers.
fit as a fiddle
in good health; in good physical condition
Ex. After making a full recovery from his plane crash, Harrison Ford, 72, was once again seen looking fit as a fiddle as he visited his office in Brentwood.
Note: Before the 19th century, the expressions “fit as a fiddle” and “fine as a fiddle” meant “appropriate for the occasion.”
to fit in (1)
to belong, to assimilate well
Ex. The pledge master warned the freshmen that if they didn’t like partying, they would not fit in.
to fit in (2)
to find time for
Ex. I’ll check my calendar and try to fit you in on Friday.
if the shoe fits
This is a shortening of “If the shoe fits, you must wear it.” The expression usually occurs as an unsympathetic response.
Ex. GEORGE: Just because I forgot her birthday, she says I don’t really care about her. ALICE: If the shoe fits…
The unexpressed thought is “If what she says is true, admit it.”
to fit like a glove
to fit perfectly
Ex. That new job fits her like a glove.
to fit the bill
to correspond to certain requirements
Ex. With your background in teaching, nursing, and music, you fit the bill for the job of camp musical director.