borrowed from New Latin abnormitas
, from abnormis
“irregular, abnormal” + Latin -itās-ity
Sparsely attested in Late and Medieval Latin—see Du Cange, who has citations from Salvian (5th century, in De Gubernatione Dei) and from a letter of Fulbert of Chartres (1021). The word abnormitas in early modern medical Latin is very likely a fresh coinage from abnormis, and the usage trajectory of the noun closely follows that of the adjective. The noun appears in treatises such as J. C. G. Ackermann's Institutiones Therapiae Generalis (1794) and August Gottlob Weber's Commentatio de initiis ac progressibus doctrinae irritabilitatis (1783). (A curious isolated occurrence is in John Merryweather's Latin translation of Thomas Browne's Religio Medici: “irregularities” in Browne's text is rendered with abnormitates.) In the vernaculars, German Abnormität appears in 1800 and is fairly common thereafter. As for English: discounting the inclusion of the word in Nathan Bailey's dictionary (and copied in innumerable dictionaries thereafter), the first textual occurrence of abnormity we have located is in The London Medical and Physical Journal, vol. 36 (July-December 1816), p. 516. Of course, abnormity is supplanted by abnormality by the second half of the 19th century.