'monstrosity' originates from Latin, specifically the word 'monstrositas', where 'monstr-' (from Latin 'monstrum') meant 'an omen or abnormal sign (often regarded as a portent or monstrous thing)'.

'monstrosity' changed from Medieval/Latinate forms such as Late Latin 'monstrositas' and Old French 'monstruosité' and eventually became the modern English word 'monstrosity'.

Initially, it meant 'a portent or unnatural occurrence (an omen)', but over time it evolved into its current meaning of 'an extremely ugly or malformed thing' and, by extension, 'something shocking, offensive, or outrageous'.