Very large, huge, or monstrous in size; extremely abnormal or irregular in form.
From Latin abnormis (ab- 'away from' + norma 'rule'). The -ous suffix (Latin -osus) creates an adjective emphasizing the quality, with the 'huge' sense possibly influenced by Latin enormis.
This is an archaic word that mostly survives in older literature and legal texts, but it beautifully shows how 'abnormal' and 'enormous' are etymologically cousins—both words emphasize deviation, one from rule, one from regular size.
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