The Collaborative International Dictionary of English v.0.48:
Fit \Fit\, n. [AS. fit strife, fight; of uncertain origin.
1. A stroke or blow. [Obs. or R.]
Curse on that cross, quoth then the Sarazin,
That keeps thy body from the bitter fit. --Spenser.
2. A sudden and violent attack of a disorder; a stroke of
disease, as of epilepsy or apoplexy, which produces
convulsions or unconsciousness; a convulsion; a paroxysm;
hence, a period of exacerbation of a disease; in general,
an attack of disease; as, a fit of sickness.
And when the fit was on him, I did mark
How he did shake. --Shak.
3. A mood of any kind which masters or possesses one for a
time; a temporary, absorbing affection; a paroxysm; as, a
fit of melancholy, of passion, or of laughter.
All fits of pleasure we balanced by an equal degree
of pain. --Swift.
The English, however, were on this subject prone to
fits of jealously. --Macaulay.
4. A passing humor; a caprice; a sudden and unusual effort,
activity, or motion, followed by relaxation or inaction;
an impulsive and irregular action.
The fits of the season. --Shak.
5. A darting point; a sudden emission. [R.]
A tongue of light, a fit of flame. --Coleridge.
By fits, By fits and starts, by intervals of action and
repose; impulsively and irregularly; intermittently.