outrageousness, monstrousness, hideousness, heinousness, horror, atrocity; villainy, cruelty, inhumanity, mercilessness, brutality, savagery, viciousness.
Wiktionary states: Enormity is frequently used as a synonym for "enormousness," rather than "great wickedness." This is frequently considered an error; the words have different roots in French, and radically different accepted meanings
As far as I can tell, the vernacular usage of enormity to which you refer is a rather recent addition to the definition, and first came into usage during the media coverage of Bush Jr's lavish inauguration, during which reporters referred to the "enormity" of the proceedings.
An adjective has rarely been abused in so fitting a way as that.
The media has repeated that usage slavishly since then.