c. 1400, "sinful, wicked;" mid-15c., "of or pertaining to a legally punishable offense, of the nature of a crime;" late 15c., "guilty of crime," from Old French criminel,criminal "criminal, despicable, wicked" (11c.) and directly from Late Latin criminalis "pertaining to crime," from Latin crimen (genitive criminis); see crime. It preserves the Latin -n-. Other adjectives include criminous (mid-15c.), criminative. Criminal law (or criminal justice) has been distinguished from civil in English at least since late 15c.
word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.
The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]
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Definitions of criminology from WordNet
the scientific study of crime and criminal behavior and law enforcement;