Origin: 1425–75; late ME
enormite < MF < L
ēnormitās. See enorm, -ty 2 
Synonyms:
1. monstrousness, heinousness. 3. hugeness, vastness.
Usage note:
3. Enormity has been in frequent and continuous use in the sense “immensity” since the 18th century: The enormity of the task was overwhelming. Some hold that enormousness is the correct word in that sense and that enormity can only mean “outrageousness” or “atrociousness”: The enormity of his offenses appalled the public. Enormity occurs regularly in edited writing with the meanings both of great size and of outrageous or horrifying character, behavior, etc. Many people, however, continue to regard enormity in the sense of great size as nonstandard.