If something is an aberration, it is not typical; it is a deviation from the standard.
- James has always been a nice guy. His bad behavior at his wife’s birthday party was an aberration.
- In Mumbai the weather is hot in May, so the heavy rain that lashed the city last week was an aberration. Rain doesn’t usually fall in May.
- My wife is a terrible cook. The good meal that you had when you visited our place last week was an aberration.
Aberrational (adjective), aberrant (adjective)
Note that an aberration is an aberrant occurrence.
- James bad behavior was aberrant.
- The heavy rain that fell in May was aberrant.
Deviation, divergence, abnormality, illusion, delusion, eccentricity