Abnormal: not typical, something out of the ordinary. 

Don’t get this word confused with its positive equivalent, exceptional

If you are abnormal, you are exceptional… in a worrisome sort of way. 

Abnormal has an interesting derivation.  Ab, of course, means away, or away from.  No surprises there.  It’s the second half of the word I find most interesting.  

In Latin, a carpenter’s square is a norma.  A carpenter uses a square to create a line, a standard, or the correct pattern.

To be abnormal, then, is to deviate from the rule, from the standard, from the carpenter’s straight line.