How do you use the word demur in a court of law?

A Demur is a method of objecting to the allegations set forth - not by denying the facts but by denying that they can sustain the pleading based on them. In other words, the facts might indicate other stronger possibilities than the one being used in the allegations.

Answer

'Demur' is the act of filing a 'demurrer' or to object to the legal sufficiency of a claim alleged in a complaint without admitting or denying the truth of the facts stated.

Used in a sentence: The defendant corporation did not demur as expected after the complaint was filed.

A 'demurrer' is the pleading that is filed with the court which, in most jurisdictions, is now called a 'motion to dismiss'.