1. A reference to something that is exceptional, uncommon, or unexpected: Sam's cat has an abnormal fear of birds.

Einstein is said to have had an abnormal IQ.

2. Descriptive of something that is unusual: An abnormal amount of snow fell in October.

Abnormal can mean either below or above normal, either better or worse than normal; while, "subnormal" always means below or worse than normal.

3. Etymology: from anormal which came from the Greek anomalos, "irregular". Later the b was added by analogy with the Latin word for irregular, abnormis, based on Latin ab-, "from" + norma, "norm"; hence "away from the norm".