fit 2 (fĭt)
a. A seizure or convulsion, especially one caused by epilepsy.
b. A sudden physical outburst: a fit of coughing; a fit of laughter.
c. A sudden, involuntary physical reaction: a fit of shivering; a fit of cramps.
d. A sudden, involuntary mental experience: a fit of amnesia; a fit of déjà vu.
2. A sudden outburst of emotion: a fit of jealousy.
3. A sudden period of vigorous activity.
by (or in)fits and starts
With irregular intervals of action and inaction; intermittently.
[Middle English, hardship, probably from Old English fitt, struggle.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.