Etymology
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corpus delicti 

1832, Latin, literally "body of the offense;" not "the murder victim's body," but the basic elements that make up a crime, which in the case of a murder includes the body of the victim. For first element, see corpus. With delictum "a fault, offense, crime, transgression," etymologically "a falling short" of the standard of law, neuter singular of past participle of delinquere "to fail; be wanting, fall short; offend" (see delinquent).

Thus, a man who is proved to have clandestinely buried a dead body, no matter how suspicious the circumstances, cannot thereby be convicted of murder, without proof of the corpus delicti--that is, the fact that death was feloniously produced by him. [Century Dictionary]
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third degree (n.)

"intense interrogation by police," 1900, probably a reference to Third Degree of master mason in Freemasonry (1772), the conferring of which included an interrogation ceremony. Third degree as a measure of severity of burns (most severe) is attested from 1866, from French (1832); in American English, as a definition of the seriousness of a particular type of crime (the least serious type) it is recorded from 1865.

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cherchez la femme 

French, literally "seek the woman," the reflexive notion that a woman or passion for one is behind whatever crime has been committed, first used by Alexandre Dumas père in "Les Mohicans de Paris" (1864) in the form cherchons la femme. French chercher is from Latin circare, in Late Latin "to wander hither and thither," from circus "circle" (see circus).

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